Kabul, Afghanistan (CNN) -- The investigation into the suicide bombing that killed 17 people on Saturday suggests it was the work of the Pakistan-based Haqqani network, an Afghan official said Monday.
"We have some contacts and some evidence on the ground and some information about the vehicles used and the people used," Interior Ministry spokesman Sediq Sediqqi said, stressing that the results of the investigation were preliminary.
"This is another sophisticated attack by the operatives of the Haqqani network, and we are also optimistic to arrest some of their operatives in Kabul in the days ahead," he said.
However, a spokesman for international forces in Afghanistan, which lost nine troops in the attack, said they have no indications yet that the Haqqani network was involved.
"All we have seen so far is that the Taliban have claimed responsibility. That doesn't necessarily mean that it was them, but we have no other indications," said Brig. Gen. Cartsen Jacobsen. "The case has to be looked at."
Another International Security Assistance Force spokesman, Lt. Col. Jimmie Cummings, added that their intelligence at this point gave no indication of the involvement of the Haqqanis.
The Saturday attack killed 13 people in a NATO convoy and four Afghan civilians. Nine of the 13 were American, including five U.S. troops. The blast also claimed the lives of two British civilians, a Kosovo national and a Canadian soldier.
U.S. officials have been increasingly vocal about the threat posed by the Haqqani network in recent months, arguing the organization has ties to Pakistani intelligence and enjoys safe havens in the country from whence it is able to launch attacks across the border in Afghanistan.
In September, then-U.S. Joint Chiefs Chairman Adm. Mike Mullen called the Haqqani network a "veritable arm of Pakistan's intelligence."
A Pentagon report on the war in Afghanistan released last week said that the ability of insurgents to flee to safe havens in Pakistan was the biggest risk to the effort to stabilize Afghanistan after nearly a decade of war. The report singled out the Haqqani network as one that has carried out major attacks.
Founded in Pakistan to fight against the Soviet occupation of Afghanistan, the Haqqani network has been blamed for killing more than 1,000 coalition and Afghan forces, including attacks on the U.S. Embassy and other targets in Kabul.
Pakistani officials have rejected claims that they support the group, but acknowledge that they are in contact with it.
This month, U.S. Secretary of State Hillary Clinton acknowledged that U.S. representatives met with Haqqani officials to discuss the possibility of negotiations that would end hostilities.