Ryan Crocker, U.S. ambassador to Afghanistan, greets Secretary of State Hillary Clinton upon her arrival in Kabul.

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NEW: Hillary Clinton arrives in Pakistan after stern words on the need to tackle terror

Clinton: We're going to be fighting, talking and building in Pakistan

CIA chief, Joint Chiefs of Staff chairman accompanying her

Clinton says she is working toward a peaceful Afghanistan

Kabul, Afghanistan CNN  — 

Secretary of State Hillary Clinton took off her diplomatic gloves Thursday, challenging Pakistan to crack down on terrorist havens on its side of the border with Afghanistan.

In a joint news conference with Afghan President Hamid Karzai, Clinton – in unusually forceful language – laid almost all of the blame for recent terror attacks on Pakistan.

The United States, she said, knows the Haqqani terrorist network operates out of havens in Pakistan.

“We intend to push the Pakistanis very hard,” Clinton said, calling it a “time for clarity.”

“Our message is very clear: We’re going to be fighting, we’re going to be talking, we’re going to be building,” she said. “And they can either be helping or hindering. But we are not going to stop our efforts to create a strong foundation for an Afghanistan free from interference, violent conflict and one that has a chance to chart its own future.”

Secretary of State Hillary Clinton arrived in Afghanistan on an unannounced visit Wednesday, just one day after landing in Libya.

She is expected to meet with Pakistani officials, including Prime Minister Yousuf Raza Gilani and Foreign Minister Hina Rabbani Khar, to stress that transitioning to Afghan security is in the interest of Pakistan, senior officials said.

Earlier Thursday, Clinton’s focus was on Afghanistan, where she met with Karzai and other government officials for talks aimed at boosting reconciliation efforts in the nation.

The top U.S. diplomat said she was working toward a peaceful Afghanistan.

“No people in the world deserve it more,” she said.

Shortly before taking off for Pakistan, Clinton told reporters that the death of Libyan strongman Moammar Gadhafi, which at that time was not confirmed, would “add legitimacy and relief to the formation of a new government.”

Her visit to Afghanistan followed a stop in Libya, the first by a Cabinet-level American official since the ouster of the longtime strongman. She landed under tight security as forces loyal to the transitional government continued to battle Gadhafi loyalists.

Earlier Thursday, Clinton met with representatives of Afghan civil society, including human rights activists who address various issues including education, gender-based violence and youth empowerment.

“These are some of my heroes,” she said as she greeted them at the U.S. Embassy in Kabul.

Her visit comes as the nation pursues peace with the Taliban after years of insurgency.

The effort suffered a major setback following the killing of Burhanuddin Rabbani, an Afghan political figure and former president who led the peace council.

Rabbani was killed at home last month by suicide bombers posing as Taliban peace mediators.

Clinton offered condolences to Salahuddin Rabbani, the oldest son of the slain leader, who was part of a roundtable Thursday.

“He tried to do the right thing,” she said.

The United States supports Karzai and recognizes the blow to the peace effort since Rabbani’s assassination, the official said.

In addition to the reconciliation efforts, Clinton also was to discuss Pakistan’s relations with the nation and the upcoming Afghan transition.

Coalition forces are in the process of transferring security control to Afghan forces ahead of a U.S. drawdown set to be completed by the end of 2014.

The 33,000 additional American troops sent last year are scheduled to depart the war-torn country fully by September next year.

CNN’s Jamie Crawford contributed to this report.