A security alert has closed down the American consulate in the Pakistani city of Karachi.

It comes nearly two months after a bomb attack on the consulate killed 12 people - all Pakistanis.

The consulate was shut down on Monday after a nearby road was reopened to traffic, triggering security concerns, US State Department spokesman Philip Reeker said.

US officials have said the offices will be closed for an indefinite period and consulate staff were sent home on Monday.

The BBC's Zaffar Abbas reports that the decision to shut down the mission was made following intelligence reports of a possible attack.

US officials and the Pakistan police have refused to give specific details on the security threat.

June attack

On 14 June a car bomb exploded outside the US consulate, which is located on one of Karachi's main streets.

The explosion, which blew a gaping hole in the mission's perimeter wall, scattered cars across the road, smashed windows and brought down power lines.

It was the second in Karachi in a matter of weeks, after a bomb attack outside the Sheraton hotel in May killed 11 French nationals and three Pakistanis.

The continuing attacks on foreigners led the US and other countries to call for all nationals to leave the country unless their work was essential.

Security around the US consulate was stepped up, with roads surrounding the premises closed to traffic.

Last month France closed its consulate building in Karachi and moved its staff to the more secure British consulate.