The U.S. State Department has issued a heightened travel warning for Sri Lanka after last Sunday's suicide bombings that killed more than 250 people.

The department is urging Americans to "reconsider travel to Sri Lanka due to terrorism."

The U.S. has also ordered the departure of all school-age family members of U.S. government employees. And it has authorized the voluntary departure of nonemergency U.S. employees and family members.

Friday night's advisory warns, "Terrorist groups continue plotting possible attacks in Sri Lanka."

Sri Lankan authorities have blamed a local Muslim militant group for the Easter attacks on churches and hotels. The Islamic State group has also claimed responsibility, though officials are still investigating the extent of its involvement.