On Easter Sunday, Sri Lanka was rocked by a series of bombings targeting Christians at churches and hotels across the nation that claimed 290 lives and injured more than 500. Now, government officials acknowledge they failed to act on multiple warnings indicating that such an attack was imminent.

Among the hundreds killed were at least 39 tourists hailing from nations including the United States, the United Kingdom, Australia, and China. Three local officers died as well.

At least one of those warnings came 10 days prior to the attacks from a little-known Islamist group, Nations Thawahid Jaman (NTJ). None of the warnings national security forces received were relayed to the nation’s Prime Minister, Ranil Wickremesinghe, or to anyone in his cabinet. Prior to these attacks, the most criminal thing NTJ was tied to publicly was the defacing of some Buddhist statues, leading authorities to speculate that these attacks were not carried out by NTJ alone, but rather through a network of different terror cells.

“We do not believe these attacks were carried out by a group of people who were confined to this country. There was an international network without which these attacks could not have succeeded,” said Sri Lankan government spokesmen Rajitha Senaratne to the BBC.

He added the Sri Lankan government would seek assistance in its investigations from foreign governments, though he didn’t specify what nations would be asked.

U.S. intelligence officials indicated that the groups responsible for the rash of bombings across Sri Lanka were “motivated” by ISIS, but the terror organization has yet to claim responsibility for the massacre. However, ISIS has a long-standing tradition of claiming responsibility for any attacks with even tenuous ties to its command structure in order to advance perceptions of the group’s global reach, so it’s likely such a claim is forthcoming.

“We saw the warnings and we saw the details given,” Senaratne told the press. “We are very very sorry, as a government we have to say—we have to apologize to the families and the institutions about this incident.”

More explosives and detonators were found early Monday, with at least one more explosion reported but no details at press time regarding possible casualties. Officials announced another explosive device was defused near Bandaranaike International Airport in the nation’s capital on Sunday evening, and 87 more detonators discovered in a private terminal of the Colombo Central Bus Station.

Thus far, 24 people were arrested under suspicion of having some connection to the spree of attacks. As of midnight Monday, the nation declared a state of emergency, granting the military unprecedented powers to investigate and pursue others believed to have a hand in the attacks.

The bombings began at 8:45 a.m. local time, with six blasts happening in quick succession across various locations. Churches in Negombo, Batticaloa, and Colombo’s Kochchikade district were targeted during Easter mass, with other explosives going off in Shangri-La, Kingsbury, and Cinnamon Grand hotels in the nation’s capital. According to official statements, each attack was carried out by suicide bombers, with more explosions following as police raided two addresses linked to the attacks.