The warning, in separate messages to Americans from the State Department and the US embassy in Islamabad, came nine days after the department authorized the voluntary departure from Pakistan of non-essential diplomats and their families, fearing a backlash to the war.

"The US embassy has received evidence of a potential threat to American citizens and other westerners in Pakistan from terrorists posing as street vendors or beggars on busy streets," the embassy said in its notice.

"Americans are urged to avoid congested areas where these individuals could approach their vehicles. US citizens in Pakistan are reminded to maintain vigilance against possible retaliation for the war in Iraq."

A statement issued later by the State Department said there was a continued possibility of attacks on "Americans, Christian facilities and other civilian targets" and repeated the information in the embassy announcement.

The State Department added, though, that: "Private American citizens currently in Pakistan should consider departing."

US officials have been conscious that the US invasion of predominantly Muslim Iraq could expose their anti-terror ally Pakistani President Pervez Musharraf to domestic political upheaval.

There are also fears that US citizens or facilities could face reprisal attacks from terrorist groups, including the al-Qaeda network and affiliates.

Americans in Pakistan had been on the alert for months over possible new terror strikes like those which have already targeted compatriots since Washington launched its campaign against terrorism after the September 11, 2001 attacks.

Those include a March 17, 2002 attack on a church in Islamabad that killed the wife and step-daughter of a US diplomat, and the kidnapping and murder of Wall Street Journal reporter Daniel Pearl.

The US consulate in Karachi was also targeted in a car bomb attack last June.

WAR.WIRE