Americans Take Extra Precautions After Attacks Pakistan Vows Aggressive Effort To Find Gunmen Who Killed Four

Americans in the Pakistani port city of Karachi took extra precautions against possible anti-U.S. attacks Thursday, and Prime Minister Nawaz Sharif telephoned President Clinton to promise aggressive action to find he gunmen who killed four American oil company workers.

The State Department warned Americans to postpone nonessential trips to Pakistan because “the security situation in Karachi deteriorated seriously” with Wednesday’s ambush in rush-hour traffic that killed the four employees of Union Texas Petroleum Co. Two previously unknown groups separately took credit for killings.

But an official of the U.S. Embassy in Islamabad indicated the claims are not considered credible. A third group, Harkat ul-Ansar, which the State Department has declared a terrorist organization, blamed unnamed groups seeking to destabilize Pakistan.

Pakistani security officials have said members of Harkat ul-Ansar might have carried out the attack to avenge the conviction Monday in Fairfax County, Va., of Mir Aimal Kasi, a Pakistani charged with the 1993 killings of two CIA employees. The travel advisory also cited the conviction in New York on Wednesday of Ramzi Ahmed Yousef - extradited from Pakistan in 1995 - in the 1993 World Trade Center bombing.

Both convictions, the State Department warned, “make Americans potential targets of retaliatory acts by their sympathizers.” About two dozen American businessmen checked out of luxury hotels in Karachi Wednesday night. Some had gone to Pakistan’s largest city to participate in an investment seminar, which the sponsor, Merrill Lynch, canceled after the shooting. The American brokerage firm also canceled a similar seminar scheduled for Friday in Lahore, capital of central Punjab Province. The American School in Karachi, which enrolls expatriate children, remained closed for a second day. Security at foreign consulates was tightened, and local police established checkpoints around neighborhoods favored by foreigners.

The embassy warned Americans in Karachi to stay indoors. Peter Claussen, an embassy spokesman, said about 2,000 Americans live in Pakistan, concentrated in Karachi, Lahore and other large cities. Another 4,000 to 5,000 naturalized Pakistani Americans have taken up residence in the country, he said.

In his telephone call to Clinton, Sharif condemned the Karachi killings as an act of terrorism and vowed his government “will spare no efforts to track down the culprits responsible for this heinous crime,” according to an account of the conversation released by a Pakistan government spokesman. Sharif also expressed “the heartfelt sympathies and condolences of the people and government of Pakistan” and asked Clinton to convey those sentiments to the families of the four slain Americans.

Sharif dispatched Interior Minister Choudry Shujat Hussain to Karachi to convene a meeting of top security officials, including the directors of civilian and military intelligence agencies. Law enforcement sources said Hussain pressured the officials to show progress in the investigation into the killings before the arrival Sunday of Secretary of State Madeleine K. Albright on the first working visit by a U.S. secretary of state since 1983.