Pakistanis took to the streets across the country on Sunday, burning an effigy of US president Barack Obama and setting fire to American flags after 24 soldiers died in NATO air strikes.
More than 700 people gathered outside the American consulate in Karachi, the port used by the United States to ship supplies to troops fighting in Afghanistan.
They shouted ''Down with America'' and riot police were deployed near the consulate. Other demonstrations occurred in Karachi, Islamabad and the city of Multan.
Their slogans included ''Down with NATO'', ''Yankees go back'', ''Vacate Afghanistan and Pakistan'' and ''Stop drone attacks.''
Pakistan has reacted with fury over the killings by NATO helicopters and fighter jets at two military posts close to the Afghan border early on Saturday.
Islamabad has sealed its border to NATO supply convoys and is reviewing its alliance with the US and NATO.
The incident occurred at the Salala checkpoint, about 2.5km from the Afghan border, at around 2am on Saturday. Two border posts were hit.
Officials said the two posts were about 300m apart on a mountain top.
Pakistani officials said NATO had the grid references of the posts and therefore should not have fired.