Washington ? The State Department has warned that additional terrorist attacks against U.S. interests may be imminent.

And in a parallel warning to Americans not to travel in Yemen, the department said it has “credible evidence” that terrorists associated with the al-Qaida network have planned attacks there.

Sunday’s deadly attack on a Protestant church in Islamabad, Pakistan, “underlines the growing possibility that as security is increased at official U.S. facilities, terrorists and their sympathizers will seek softer targets,” according to a department release.

Such targets may include restaurants, schools, clubs and other places where Americans congregate, said the department, which recommended people avoid those areas outside the United States or be more careful when visiting them.

The department cited credible reports of possible attacks, but said it had no information on targets, timing or how the attacks may be carried out. It warned that terrorist activities may include suicide attacks and kidnapping.

“We remind American citizens to remain vigilant with regard to their personal security and to exercise caution,” the release said.

Five people were killed, including a U.S. Embassy employee and her teen-age daughter, and 45 people injured in the church attack in Islamabad.

Terrorists have always looked for “soft” targets when their primary goals military bases and government offices have proved difficult to reach.

Military bases and embassies are fortified more than ever before with high walls, concrete barriers, sophisticated cameras, armored vehicles and guards with machine guns.

Schools are one of the biggest concerns, many government and private security officials say. Private schools in many cities are often attended by the children of both official and private Americans.

Fifteen years ago, in an attack blamed on Libya, two U.S. soldiers were killed in a bombing at a West Berlin disco. In 1997, four American auditors of a U.S. oil company and their Pakistani driver were killed while traveling in Karachi, Pakistan, between their hotel and work.