CNN  — 

Sri Lanka awoke Tuesday to a day of mourning as the country continued to reel over the devastating attacks which took some 253 lives, including many Christians celebrating Easter Sunday.

Prime Minister Ranil Wickremesinghe tweeted early Tuesday morning, saying that the country grieved as one.

“Today as a nation we mourn the senseless loss of innocent lives this past Easter Sunday,” he tweeted, spelling out his gratitude for the emergency and security forces who responded to the multiple bombings that tore through three churches, three luxury hotels and two other locations.

He added that it “is imperative that we remain unified as Sri Lankans in the face of this unspeakable tragedy.”

Failure to act

On Monday the Sri Lankan government admitted that it failed to act on multiple warnings before a coordinated series of attacks ripped through churches and hotels on Easter Sunday, adding that an international terror group might be to blame.

A government spokesman, Rajitha Senaratne, revealed that warnings were received in the days before the attacks, including from foreign intelligence services.

He said one of the warnings referred to National Tawheed Jamath, or NTJ, a little-known local Islamist group that defaced Buddhist statues in the past. But Senaratne, who is also health minister, said he did not believe a local group could have acted alone.

“There must be a wider international network behind it,” he said.

No group has yet claimed responsibility.

Four days after the coordinated attacks, the Sri Lankan Health Ministry revised the death toll, saying 253 people had died. That toll is significantly lower than the 359 initially reported to CNN by a Colombo police spokesman this week. The health ministry cited the condition of remains and the difficulty in identifying them for the discrepancy.

The United States believes it has identified a key terrorist operative in the attacks, and has initially concluded that the person has connections to international terrorism organizations, including ISIS, two US officials directly familiar with the initial US intelligence assessment said.

These connections are a key reason the US has come to an early conclusion the attacks were inspired by ISIS, according to one of the two officials. For now, the US is trying to figure out just how involved ISIS may have been in facilitating the attacks, the official said.

One of the blasts tore through St. Sebastian's Church in Negombo, north of Colombo.

Sri Lankan government apologizes

Police arrested 24 people in connection with Sunday’s attacks, the worst violence the South Asian island has seen since its bloody civil war ended 10 years ago.

Six suicide bombers were involved, Sri Lanka military spokesman Sumith Atapattu said. Nine of the 24 suspects have been remanded until May 6 by a Colombo magistrate, state media reported.

The security situation remained fluid on Monday.

Police found 87 detonators in a private terminal of the main bus station in Sri Lanka’s capital, Colombo, and a controlled explosion was carried out on a van near St. Anthony’s church, one of three churches targeted in the attack. On Sunday evening, an improvised explosive device was defused near the capital’s Bandaranaike International Airport.

A dusk-‘til-dawn curfew was imposed for the second night in a row. Sri Lankan authorities declared a state of emergency from midnight Monday, and said Tuesday would be a national day of mourning.

Intelligence failures would be investigated, Senaratne said.

“We saw the warnings and we saw the details given,” he told reporters. “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.” Families would be compensated and churches rebuilt, he said.

The political situation in Sri Lanka

The blasts appears to have targeted tourism hotspots, as well as churches, in an effort to gain maximum global attention.

Most of the dead and injured were Sri Lankan. At least 31 tourists were killed in the attacks, according to a statement released on Monday evening from Sri Lanka’s Ministry of Foreign Affairs, which revised down the Sri Lankan tourism minister’s previous estimate of 39 people.

The attacks occurred in a period of political instability in Sri Lanka.

In October, the Sri Lankan President attempted to depose the prime minister and replace him with a favored successor. That move backfired and Prime Minister Ranil Wickremesinghe was reinstated in December.

President Maithripala Sirisena was out of the country at the time of Sunday’s attacks.

Wickremesinghe said warnings about a potential attack had not been shared with him or other government ministers. Sajith Premadasa, minister of housing construction and cultural affairs, said security officers were guilty of “negligence and incompetence.”