"The consulate is closed today because of heightened security concern," said US embassy spokesman Greggory Crouch.

"We have credible information to increase our security."

The consulate in Karachi, Pakistan's biggest city and the country's commercial hub, has been a target before. A car bomb killed 12 Pakistanis outside the consulate in June 2002.

Americans had also been told to avoid the area around the consulate, which was hit by a massive suicide bomb attack nearly three years ago, and the nearby Marriott hotel, an official said.

"The consulate is closed today," Greggory Crouch told AFP. "We have received credible information of a threat and that has heightened our security concern."

The consulate was closed on the orders of the consul general, Douglas Rohn, said Crouch.

"It is my understanding that the staff were sent home," he added.

"We expect it will resume normal operations tomorrow."

A staff member at the consulate in the southern port city, speaking on condition of anonymity, also confirmed it was closed for the day.

Police have closed all roads around the US consulate and the road leading to the residence of the consul general.

In June 2002, a suicide car bomb blast outside the consulate killed 12 Pakistanis.

Last year two successive car bombs near the consul general's residence killed one policeman and injured more than a dozen press photographers.