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Kabul, Afghanistan (CNN) -- The performance of Afghan forces in reacting to a series of sustained assaults shows that the country's security situation will not deteriorate after the departure of international troops scheduled for next year, President Hamid Karzai said Monday.
"I'm rather very confident that once the international forces leave, that the Afghan forces will be able to defend their country as they demonstrated yesterday," Karzai told CNN's Christiane Amanpour.
Afghan security forces took the lead in responding to a coordinated wave of assaults in Kabul and across eastern parts of Afghanistan on Sunday and Monday.
Afghan troops completed the final raids Monday, clearing two central Kabul buildings of holdout insurgents, a NATO spokesman said.
Afghan forces also captured a suicide bomber Monday in Kabul before he was able to reach his target, NATO spokesman Lt. L.M. Rago said. Two other would-be bombers were captured on Sunday, according to Rago.
Karzai said that four insurgents were in custody.
The nearly 18-hour series of assaults left four civilians and eight members of the Afghan security forces dead, Interior Minister Bismillah Mohammadi said Monday. About 65 people were wounded, he said.
One insurgent told officials that he was working for the Haqqani network, a ruthless, well-trained organization linked to al Qaeda, Mohammadi said.
The coordinated attacks were the most dramatic and widespread assault in the Afghan capital since an attack in September on the U.S. Embassy and NATO headquarters.
The United States had intelligence that the Haqqani network was planning a high-profile attack in Afghanistan, U.S. Defense Secretary Leon Panetta said Monday.
And Pentagon spokesman George Little went further, saying the group appeared to be behind the wave of attacks.
Little would not discuss specific intelligence. But he said the well-coordinated attacks appeared to have the hallmarks of previous attacks by the Haqqani network, which has long aimed its attacks at Kabul.
Given the seasonal rise in attacks as the warmer weather of spring approaches, Little said, U.S. officials "thought something like this may very well happen and it did."
Little emphasized the United States had not had a "precise understanding" of when and where such attacks might come.
While the Haqqani group is based in Pakistan, at the moment the United States does not have evidence that the attacks emanated from there, Gen. Martin Dempsey, chairman of the Joint Chiefs of Staff, said Monday.
Karzai said the attacks represented an intelligence failure for Afghanistan and especially its allies in NATO.
"I'm not blaming NATO for this," he said. "I'm simply asking a question as to the efficiency of our intelligence gathering systems."
Insurgents launched the wave of audacious attacks in Kabul and three other areas of the country Sunday. Government forces said they had repelled the offensives, but some of the violence in the streets of the capital spilled into Monday.
Explosions rocked central Kabul early Monday after periodic bursts of gunfire that lasted well into Sunday night in the district that houses government offices and allied embassies.
"In Kabul, our problem was that we were very cautious not to cause any civilian casualty, therefore it took us longer to act," Mohammadi said Monday.
He said that more than 30 people had been trapped by fighting around the Afghan parliament and that it had taken until Monday morning to rescue them.
Thirty-five of the insurgents died in the violence, most of them killed by government forces, Mohammadi said. Only a few succeeded in detonating explosives attached to their bodies, he said.
Karzai said the attacks demonstrated the capability of Afghan forces.
"As brazen as it looked, it was a failure from our perspective, because our security forces responded immediately and quite efficiently," Karzai said.
Afghan forces won praise for their response not only from Karzai, but also from Gen. John Allen, the U.S. and NATO commander in Afghanistan.
Allen said Sunday that the Afghans beat back the insurgents without allied assistance.
"They were on scene immediately, well-led and well-coordinated," Allen said. "They integrated their efforts, helped protect their fellow citizens and largely kept the insurgents contained." He said the attacks were meant to signal "that legitimate governance and Afghan sovereignty are in peril," but the Afghan response "is proof enough of that folly."
The majority of the attackers used women's clothing -- with burqas covering their faces -- in order to reach their intended positions, Mohammadi said.
They even "had bunches of flowers in their car in Kabul in order to show off that they were women and they were going to a wedding party or something like that," he said.
The Taliban militia that once ruled most of Afghanistan claimed responsibility for the attacks, saying it launched fighters into battle with suicide vests, rocket-propelled grenades and hand grenades in Kabul and the provinces of Nangarhar, Paktia and Logar.
However, one of the attackers was arrested in Nangarhar on Sunday and said during questioning that he was part of the Haqqani network, supporting the view of several observers who doubted the Taliban had the capacity to mount such offensives alone.
The Haqqani network has operated for more than 20 years and played a significant role among the mujahedeen groups that fought Soviet occupation of Afghanistan. It is currently led by Sirajuddin Haqqani and is regarded by U.S. military commanders in the region as one of the most effective and dangerous arms of the insurgency.
A recent paper by the nonpartisan Institute for the Study of War described the Haqqani network as "Afghanistan's most capable and potent insurgent group."
According to the report, the Haqqanis "continue to maintain close operational and strategic ties" with al Qaeda and its affiliates.
The paper's authors said the network had "expanded its reach" toward the Taliban's traditional strongholds in southern Afghanistan, the areas surrounding Kabul and the north of the country.
Senior U.S. officials have persistently accused elements in Pakistan's military intelligence service of aiding the Haqqanis as a way of ensuring Pakistani influence in Afghanistan.
The officials says that both the Taliban and the Haqqani network have safe havens in Pakistan that they use to launch cross-border attacks on U.S. troops in Afghanistan.
Apparently supporting that point, the insurgent arrested Sunday in Nangarhar said he had been trained and equipped "on the other side of the border," Mohammadi said.
A senior official with Pakistan's intelligence service said officials were concerned the attacks may be used to pressure Pakistan either to attack north Waziristan, where the Haqqani network has operations, or to allow a return to a broader U.S. campaign of drone strikes against militant targets.
U.S. Ambassador Ryan Crocker earlier had said he thought the attacks Sunday might have been the work of the Haqqani network rather than the Taliban.
"The Taliban are very good at issuing statements, less good at fighting," Crocker said. No Americans were hurt during the fighting, he said.
NATO's International Security Assistance Force said that as many as seven locations in Kabul were attacked, including the parliament building and the American, German and Russian embassies.
Sediq Seddiqi, a spokesman for the Afghan interior ministry, said Sunday that the insurgents had taken up positions in empty buildings in three Kabul districts to carry out the attacks. The Kabul police said they found and detonated a van full of explosives.
Meanwhile, an airbase used by U.S. troops in the eastern city of Jalalabad, in Nangarhar Province, also came under attack, NATO command in Kabul reported. Four suicide bombers wearing women's burqas tried to attack the Jalalabad airfield where U.S. troops are based, airfield commander Jahangir Azimi said.
At least three of the attackers were killed, ISAF said in a statement.
Separately, a group of suicide bombers attacked the police training center in the city of Gardez, in Paktia Province. At least eight civilians were wounded, said a police official at the center, who was not authorized to speak to the media and asked not to be identified.
And 15 would-be attackers were arrested in Kunduz Province plotting similar strikes, said Lal Mohammad Ahmadzai, a spokesman for the chief of police for north and northeast Afghanistan.
The Taliban, the Islamist militia that once ruled most of Afghanistan, said the attacks were in retaliation for the killing of 17 Afghan civilians in Kandahar province last month. A U.S. Army staff sergeant, Robert Bales, has been charged with those killings.
But Jeff Dressler, an expert on the Haqqani network at the Washington-based Institute for the Study of War, said that the coordination seen in the Kabul attacks indicates a Haqqani-led network was behind them and that the planned but disrupted attacks in the north may also have been Haqqani-linked.
"This is likely their unofficial announcement marking the start of the spring fighting season," Dressler said. Though the attacks didn't succeed, he said, "The target selection was likely intended to send a message to the U.S., U.K., Russia and the Afghans that this will in fact be a bloody year for all forces in Afghanistan, particularly the east of the country."
U.S. Embassy spokesman Gavin Sundwall said he could not confirm that the embassy itself was the target of the attacks but said gunfire had been heard in the vicinity. In a statement from London, Foreign Secretary William Hague said the British Embassy was one of the targets, but "every member of embassy staff is safe."
"The Afghan National Security Forces responded to the attacks bravely, promptly and effectively, once again illustrating the significant progress that has been made in ensuring that Afghans can look after their own security," Hague said. The embassy premises sustained "limited damage," he said, and its staff "dealt with this dangerous situation extremely professionally."
Several rocket-propelled grenades landed in the compound of the Japanese Embassy, a spokesman for the Japanese Ministry of Foreign affairs said. Embassy staff members were moved to the compound's underground air-raid shelter. No one was wounded, the spokesman said.
India also said it had no reports of its citizens being wounded.
CNN's Masoud Popalzai, Barbara Starr and Nick Paton Walsh contributed to this report.