COLOMBO, Sri Lanka >> The death toll from the Easter suicide bombings in Sri Lanka rose to 359, police said Wednesday, as the country’s leaders vowed to overhaul the security apparatus amid a series of intelligence lapses before the attacks.

U.S. Ambassador Alaina Teplitz, meanwhile, told reporters that “clearly there was some failure in the system.” Sri Lanka’s leaders have said some of the country’s security units were aware before Easter of possible attacks, but did not share those warnings widely.

Teplitz said the U.S. had “no prior knowledge” of a threat before the bombings. She said a team of FBI agents and U.S. military officials were helping in the investigation.

The Islamic State group has claimed responsibility and released images that purported to show the seven bombers who blew themselves up at three churches and three hotels Sunday in the worst violence this South Asian island nation has seen since its civil war ended a decade ago.

The government has said the attacks were carried out by Islamic fundamentalists in apparent retaliation for last months’ New Zealand mosque massacre but has said the seven bombers were all Sri Lankan. Prime Minister Ranil Wickremesinghe said investigators were still working to determine the extent of the bombers’ foreign links.

Police spokesman Ruwan Gunasekara said Wednesday morning that 18 additional suspects were arrested overnight, raising the total detained to 58.

The Islamic State group has lost all the territory it once held in Iraq and Syria and has made a series of unsupported claims of responsibility around the world.

Sri Lankan authorities have blamed a local extremist group, National Towheed Jamaar, whose leader, alternately known as Mohammed Zahran or Zahran Hashmi, became known to Muslim leaders three years ago for his incendiary speeches online.

Teplitz declined to discuss whether the embassy or U.S. officials had heard of National Towheed Jamaar or its leader prior to the attack. “If we had heard something, we would have tried to do something about this,” Teplitz said.

The Islamic State group’s Aamaq news agency released an image purported to show the leader of the attackers, standing amid seven others whose faces are covered. The group did not provide any other evidence for its claim, and the identities of those depicted in the image were not independently verified.

Meanwhile, in an address to Parliament, Ruwan Wijewardene, the state minister of defense, said “weakness” within Sri Lanka’s security apparatus led to the failure to prevent the nine bombings.

“By now it has been established that the intelligence units were aware of this attack and a group of responsible people were informed about the impending attack,” Wijewardene said. “However, this information has been circulated among only a few officials.”

In a live address to the nation late Tuesday, Sri Lanka President Maithripala Sirisena said he also was kept in the dark on the intelligence about the planned attacks and vowed to “take stern action” against the officials who failed to share the information. He also pledged “a complete restructuring” of the security forces.

Wijewardene said the government had evidence that the bombings were carried out “by an Islamic fundamentalist group” in retaliation for the March 15 mosque shootings in Christchurch, New Zealand, that killed 50 people, although he did not disclose the evidence.

New Zealand Prime Minister Jacinda Ardern told reporters in Auckland on Wednesday that she’d had no official word from Sri Lanka, or seen any intelligence reports, to back that up. However, she added that Sri Lanka was in the early stages of its investigation.

An Australian white supremacist was arrested in the Christchurch shootings.

The history of Buddhist-majority Sri Lanka, a country of 21 million including large Hindu, Muslim and Christian minorities, is rife with ethnic and sectarian conflict.

In the 26-year civil war, the Tamil Tigers rebel army had little history of targeting Christians and was crushed by the government in 2009. Anti-Muslim bigotry fed by Buddhist nationalists has swept the country recently but Sri Lanka has no history of Islamic militancy. Its small Christian community has seen only scattered incidents of harassment.