Pakistan has lodged a strong protest with Washington over the killing of two of its soldiers by US troops on the border with Afghanistan.

This was the first time that troops from Pakistan, considered Washington's front-line ally in the war against terror, were killed by US soldiers.

The issue is also likely to be raised during the meeting in Kabul of the  tripartite commission -- which includes Pakistani, Afghan and US officials -- set up to discuss the situation on the ill-defined border.

The commission was formed after Afghanistan accused Pakistani troops of making repeated incursions into Afghan soil under the pretext of chasing fleeing Al Qaeda and Taliban fugitives.

The two soldiers were killed and another injured when American troops in Afghanistan called in air support to counter attackers who had fired at their patrol and fled towards the border.