A local Islamist terrorist group called National Thowfeek Jamaath was responsible for multiple Easter Sunday suicide bomb attacks against Christians and luxury hotel guests in Sri Lanka, government officials on Monday revealed.

Health Minister Rajitha Senaratne told a news conference that all the bombers were Sri Lankan citizens. Earlier, a government forensic crime investigator said an examination of the Islamist attackers’ body parts showed that they were suicide bombers.

Senaratne, who is also a Cabinet minister, added that the government was investigating whether the group had “international support”.

Meanwhile, Sri Lankan President Maithripala Sirisena will declare a nationwide emergency from midnight on Monday, his office said.

“The government has decided to gazette the clauses related to prevention of terrorism to emergency regulation and gazette it by midnight,” the president’s media unit said in a statement.

“This is being done to allow the police and the three forces to ensure public security,” the statement outlined, referring to the army, navy and air force.

The U.S. State Department, meanwhile, warned of further attacks in a revised travel advisory, urging increased caution and adding: “Terrorist groups continue plotting possible attacks in Sri Lanka.”

The bombings, Sri Lanka’s deadliest violence since a devastating civil war ended a decade ago on the island nation, killed at least 290 people with more than 500 wounded, on Easter Sunday.

Most of those killed were Sri Lankans. But the three bombed hotels and one of the churches, St. Anthony’s Shrine, are frequented by foreign tourists, and Sri Lanka’s Foreign Ministry said the bodies of at least 27 foreigners from a variety of countries were recovered.

The blast at St Anthony’s Shrine, an historic Catholic Church, was so powerful that it blew out much of the roof, leaving roof tiles, glass and splintered wood littering the floor that was strewn with bodies.

AP, AFP contributed to this story