Four U.S. Citizens Have Been Killed in Karachi, Pakistan; The Killings Follow Yesterday's Conviction of a Pakistani Man for Killing Two CIA Agents

Details of the shooting were sketchy but it is believed that the four Americans worked for an international oil company.

No one has claimed responsibility for the killing in the violence-wracked southern port but it comes a day after a Pakistani, Mir Aimal Kasi, was convicted in a U.S. court of killing two CIA agents in Washington.

On Tuesday, the U.S. State Department issued a warning to Americans in the region to watch out for possible retaliation following the conviction.

Prosecutors claim Kasi, who also wounded three others in the 1983 shooting, was out to avenge the bombing of Iraq and American meddling in Muslim countries.

Frank Darling, 28, and Lansing Bennett, a 66-year-old physician employed by the CIA, were in their cars waiting in morning traffic outside the agency when Kasi walked between cars, firing an AK-47 assault rifle.

The identity of the Americans in Wednesday's shooting had not been released but it appeared the van carrying the victims was somewhere near the Arabian Sea harbor port when the gunmen opened fire.

The sources said the American workers were apparently en route to their office in the Beharia Complex about a half-mile from a downtown hotel where they were staying when the gunmen fired on them.

Other details were not immediately known.