US Secretary of State Hillary Clinton pressed Pakistan to take action against Haqqani militants the United States blames for an attack on the US embassy in Kabul, officials said.
Clinton met in New York with Pakistani Foreign Minister Hina Rabbani Khar for 3.5 hours of "very substantial" and "very candid" talks that began and ended with counter-terrorism, Clinton spokeswoman Victoria Nuland said.
A senior State Department official also told reporters on condition of anonymity that the talks began and ended with concerns about the Taliban-allied Haqqani network Washington suspects receives Pakistani government support.
The September 13 attack on the US embassy in Kabul, which left 15 dead, "changed the nature" of the previously planned gathering, which lasted longer than expected, according to the official.
Meeting on the sidelines of the UN General Assembly, Khar made clear to Clinton that Pakistan "couldn't condemn more" the attack, adding "that this kind of terrorism was a threat to Pakistan" as well, the official said.
"We were specific about the need for Pakistan to take action on the Haqqani network."
The Pakistanis "understand the threat the Haqqanis pose to them," and that "it is time" for them to take action, he said when asked about the Pakistani reaction," according to the senior US official.
Cameron Munter, the US ambassador in Islamabad, bluntly cited evidence Saturday linking the Pakistani government to the Haqqani network of militants, blaming the group for the Kabul siege.
But the US official said the "evidence" was not raised in Clinton's talks with Khar.
US Defense Secretary Leon Panetta has warned that the United States would retaliate against Pakistan-based insurgents.
Washington has long urged Pakistan to take action against the Haqqani network and suspected the group enjoys support within Pakistan's feared intelligence services.
But the public comments are a mark of strained ties between the fragile anti-terror allies, with relations fractious since the US raid in Pakistan that killed Al-Qaeda leader Osama bin Laden in May, without Washington first informing Islamabad.
The Haqqani network is thought to have been behind some of the deadliest attacks in Afghanistan, where NATO plans a gradual withdrawal of troops after a gruelling 10-year war.
Militants frequently cross the porous Afghan-Pakistani border and the Haqqanis, who are closely allied with Pakistani and Afghan Taliban and also linked to Al-Qaeda, only launch attacks in Afghanistan.