Pakistan is said to be pulling out of an international conference on the future of Afghanistan, after 24 of its soldiers were killed in a cross-border attack by NATO forces.
The incident, which happened on Saturday, has fuelled a wave of anti-American sentiment, with protests taking place throughout Pakistan.
The conference boycott comes after NATO supply routes were shut down.
The move has left hundreds of trucks stranded in Pakistan.
Convoys carry almost half of the alliance's supplies overland to troops in Afghanistan.