April 22 (UPI) -- Sri Lanka declared a state of emergency Monday and the U.S. Federal Bureau of Investigation is aiding in the investigation of the suicide bomb attacks that killed nearly 300 people and injured hundreds more.
Several bombers carried out six coordinated attacks at churches and hotels Sunday, killing at least 290 people. Sri Lankan authorities said two dozen people have been arrested, and they identified local Islamist militant group National Thowheed Jamath as being responsible for the blasts.
The government declared a state of emergency to take effect at midnight Monday. The declaration allows police and military forces to detain and interrogate potential suspects without a court order. Officials also said a curfew would remain in effect for another night.
Presidential chief of staff Hemasiri Fernando said the FBI is aiding in the Sri Lankan inquiry after a phone call Monday between U.S. President Donald Trump and Sri Lankan Prime Minister Ranil Wickremesinghe.
"President Trump pledged United States support to Sri Lanka in bringing the perpetrators to justice, and the leaders re-affirmed their commitment to the fight against global terrorism," White House deputy press secretary Hogan Gidley said in a statement. "Wickremesinghe expressed appreciation for the President's concern and updated him on the progress of the investigation."
A new explosion was heard in the capital of Colombo Monday as police attempted to defuse explosives in a suspicious van near another church. The explosion knocked down a security officers and blew out the windows on the street, but no serious injuries were reported.
U.S. Secretary of State Mike Pompeo said several Americans died but the exact number wasn't immediately known. He said the bombings underscore that "radical Islamic terror remains a threat." CNN reported a Washington, D.C., boy was among the dead, citing an email from the Sidwell Friends private school.
Sri Lanka officials said foreign agencies had warned of the plot and some of those arrested, along with some of the bombers, were named in the intelligence reports. Sri Lankan officials said, however, they have doubts the attacks were carried out by the National Thowheed Jamath group without help. Justice minister Rauf Hakeem said "such sophisticated" attacks could not have been achieved by the local Islamist group alone.
More than 1,000 worshipers were packed inside the St. Sebastian church when explosions went off Sunday during the Easter service. There were nine total bomb blasts, officials said. The Cinnamon Grand, the Shangri-La Hotel and the Kingsbury Hotel, all in Colombo, were attacked, along with St. Sebastian's Church in Negombo, St. Anthony's Shrine in Kochchikade and Zion Church in Batticaloa.
"We never expected such a thing to happen, especially in a place of religious worship," Bishop J.D. Anthony said Monday. "This church is in a very rural area so we never expected this to happen here ... Innocent people who came to pray here ... they sacrificed their life for God."
Police spokesman Ruwan Gunasekara said citizens of Poland, Denmark, China, the United States and other nations were among the dead. Australian Prime Minister Scott Morrison tweeted Monday two Australians were killed and two were injured.
I can also confirm two other Australian citizens were injured in the attacks. They have received medical treatment for their injuries and are recovering. My thoughts and prayers are with the family and friends of those who have passed away and the injured.— Scott Morrison (@ScottMorrisonMP) April 22, 2019
Wickremesinghe condemned the attacks as "cowardly.'
"I call upon all Sri Lankans during this tragic time to remain united and strong," he posted to Twitter.
The attacks prompted some U.S. authorities to boost security. The New York City Police Department increased its presence around places of worship following the attack, Chief Terence Monahan said.
"Although there is no known nexus to NYC, NYPD officers will be seen at temples and churches as we remain steadfast in our mission to keep every New Yorker safe," he wrote.
The U.S. State Department issued a travel advisory for Sri Lanka in the wake of the attacks.
"Terrorists may attack with little or no warning, targeting tourist locations," the U.S. Embassy in Sri Lanka wrote.
United Nations Secretary-General Antonia Guterres said he was "outraged" by the bombings and called for the plotters to be "swiftly brought to justice."
The Indian Coast Guard was placed on high alert in Palk Strait, the narrow sea channel between Sri Lanka and India, to watch for perpetrators fleeing the island.
More than 7 percent of Sri Lanka's population of 24.1 million is Christian. Seventy percent identify as Buddhist, 12 percent Hindu and 9.7 percent Muslim. The country has seen a decade of lasting violence after the end of its 25-year civil war in 2009. More than 100,000 civilians and 50,000 fighters died in the conflict.