A senior American envoy has met with Hina Rabbani Khar, the Pakistani foreign minister, in Islamabad, as part of efforts to get Pakistan to reopen US and NATO supply routes to Afghanistan.
Speaking to reporters after the meeting on Thursday, Marc Grossman, the US special envoy for Afghanistan and Pakistan, said the main purpose of his trip was to get the "ground lines of communications reopened".
Grossman said he did not expect to receive an immediate commitment that the routes would reopen - but that "the task now is to begin a conversation about how to move forward".
Islamabad shut the supply lines in November in protest against an inadvertent US air raid that killed 24 Pakistani troops.
Pakistan's parliament has also demanded that Washington apologise for the border incident and halt attacks by drone aircraft against armed fighters in northwest Pakistan.
Grossman repeated earlier US statements of regret but did not apologise.
Jalil Abbas Jilani, Pakistan's foreign secretary, said Islamabad's previous agreement with the US regarding the supply lines for NATO troops are no longer valid and that the two countries need to agree on a new arrangement.
Earlier this month, Pakistan's parliament unanimously approved new guidelines - a decision that could pave the way for the reopening of supply lines to NATO troops in Afghanistan.
The guidelines call for NATO and the US to pay Pakistan more for the right to ship supplies across its soil and stipulate that no arms or ammunitions be transported.
Western forces have only ever trucked fuel and other nonfatal supplies across Pakistan because of the risk that they could fall into the hands of insurgents.
About 30 per cent of supplies used by NATO and US troops in landlocked Afghanistan are transported through Pakistan.