By Euan McKirdy, Sheena McKenzie, Caitlin Hu, Lauren Said-Moorhouse, Harmeet Kaur, Jessie Yeung and Meg Wagner, CNN
From CNN's Barbara Starr, Pentagon correspondent
The initial intelligence indications are that the group responsible for the attacks in Sri Lanka was inspired by ISIS, a US official has told CNN.
At this point, no group has claimed responsibility for the attacks.
The official said at least four US citizens have been killed.
It was unclear if the US death toll included the two dual US-UK nationals who were among the eight UK nationals confirmed dead.
A day after a series of coordinated blasts rocked Sri Lanka, officials still appear to be trying to get a handle on the situation on the ground.
What the investigation has turned up so far on Monday:
Hours after the initial blasts, a six-foot-long pipe bomb was found on Sunday night near the road leading to Sri Lanka’s Bandaranaike International Airport.
With the situation in flux, residents are preparing to hunker down for the night as a curfew comes into effect across the island from 8 p.m. (10 a.m. ET) until 4 a.m. (6 p.m. ET). It's the second night Sri Lankans have been asked to remain indoors after sunset.
From CNN’s Bharti Naik in London
At least 39 tourists were killed in the Sri Lanka bombings on Easter Sunday, the country’s tourism minister said on Monday.
John Amaratunga, the minister of tourism, wildlife and Christian religious affairs, also confirmed 28 tourists are currently receiving hospital treatment following the attacks.
“I wish to assure the tourism industry that the government has taken every possible measure to ensure the safety of the public and all tourists who are in the country. The three armed forces along with the police have put in place a comprehensive security plan covering hotels, resorts and places of tourist interest,” Amaratunga said in a statement.
From CNN's James Griffiths in Katuwapitiya
A bishop at the St. Sebastian church -- one of the sites targeted in Sri Lanka on Easter Sunday -- told CNN he would have never dreamt that his community's house of worship might be targeted in an attack.
"We never expected such a thing to happen, especially in a place of religious worship,” Bishop JD Anthony said Monday. “This church is in a very rural area so we never expected this to happen here.”
He suggested the attacker might have chosen the church because of the large number of people who attend the services here. On the morning the bomb went off, more than 1,000 worshipers had gathered for the Easter service.
“We have more than 100 people who were killed on the spot and so many others injured. We are still in an atmosphere of shock.”
He said they don’t know what to do, “only to pray, that is our most important and powerful weapon.”
“I fear the motive of doing this” might be to increase community tensions, though he added “we never had” this type of attack previously.
“I couldn’t sleep because of this. Innocent people who came to pray here ... they sacrificed their life for god.”
From CNN's Jenni Marsh and Julia Hollingsworth in Hong Kong
The Sri Lankan government has admitted it failed to act on multiple warnings before a coordinated series of attacks ripped through churches and hotels on Easter Sunday, and said it feared an international terror group might have been behind the atrocities.
A government spokesman, Rajitha Senaratne, said multiple warnings were received in the days before the attacks, which killed 290 people and injured at least 500 more. CNN understands that at least one warning referred to Nations Thawahid Jaman (NTJ), a little-known local Islamist group which has previously defaced Buddhist statues.
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.
There were also fears of more devices following the attack. A ninth improvised explosive device (IED) was defused near the capital’s Bandaranaike International Airport on Sunday evening. And on Monday, police found 87 detonators in a private terminal of the main bus station in the capital Colombo.
From CNN's Ivan Watson in Colombo
Sri Lankan police performed a controlled detonation Monday of a suspicious van near St. Anthony’s church, which was one of the churches targeted in Sunday’s coordinated attacks in Colombo.
CNN’s Ivan Watson is at the scene and described the explosion as “a very big blast” which “knocked down a security officer” and blew out the windows in the street.
Police have pushed onlookers back and established a cordon around the site.
From CNN's Gianluca Mezzofiore
Britain's Queen Elizabeth has released a message expressing her sadness over the Sri Lanka Easter Sunday attacks.
Here's the 93-year-old monarch's full statement:
“Prince Philip and I were deeply saddened to learn of the attacks in Sri Lanka and send our condolences to the families and friends of those who have lost their lives.
I pay tribute to the medical and emergency services who are providing support to those who have been injured. Our thoughts and prayers are with all Sri Lankans at this difficult time.
Elizabeth R.”
From CNN's James Griffiths in Katuwapitiya
It should have been a normal Sunday service. Hundreds had turned out for Easter Sunday and Sanjeewa Appuhamy, an assistant priest at St. Sebastian's church, was almost the end of morning's celebrations. Then a bomb exploded.
"I heard a big noise,” Appuhamy told CNN. He did not see the bomb but when the dust cleared, the church looked like a disaster site.
“Broken glass, dust, all of a sudden covered all the church. People were shouting, weeping, we didn’t know what was happening," the priest added.
Appuhamy added: “We can build up our church but we cannot build up their lives.”
From CNN's Ivan Watson in Colombo, Sri Lanka
Sri Lankan authorities investigating the devastating blasts across the country on Easter Sunday have found 87 detonators in the capital.
Ruwan Gunasekara, assistant superintendent of police and spokesperson, told CNN that police found the detonators in a private terminal of the Central Bus Stand in Colombo Monday.