Yousuf Reza Gilani spoke to a gathering of political and military leaders trying to formulate a response to US allegations that the army's spy agency is supporting the insurgents.
The claims last week by Admiral Mike Mullen, the US's top military officer, sent relations between Islamabad and Washington plummeting and triggered a nationalist, anti-American backlash across Pakistan.
Much of the focus has been on veiled US threats of unilateral action against Afghan militants sheltering on the Pakistan side of the border.
"Pakistan cannot be pressured to do more, but the doors are still open from our side for talks and discussion," said Mr Gilani.
The intelligence chief, Lt General Ahmed Shuja Pasha, was also scheduled to address the gathering, which was closed to the media.
US officials have long talked with Islamabad about links between Pakistan and the Haqqani network that is behind much of the violence in Afghanistan.
Those discussions were mostly held in private, in the hope that Pakistan could gradually be persuaded to sever the purported ties with the group.
But Admiral Mullen seemed to signal a new approach last week when he told Congress that that Haqqani network was a "veritable arm" of the spy agency, which he said supported the militants in a recent attack on the US embassy in Kabul.
Pakistani officials have denied the allegations and accused Washington of making them a scapegoat for US failures in Afghanistan.
Most of Pakistan's feuding political party leaders were present at yesterday's meeting, a sign of how US threats can unite them.
The attendants are expected to issue a resolution condemning the US but it is unclear whether the statement will touch on the allegations of Pakistan support for Afghan militants, a far more sensitive topic because it could set off criticism of the army.