The death toll from the Sri Lanka Easter Sunday explosions now stands at 207 with 450 people injured, a police spokesman has said.
The blasts caused fatalities among worshippers and guests at three churches and three hotels.
A total of eight explosions are understood to have taken place with two of them suspected to have been carried out by suicide bombers.
Britain’s High Commissioner to Sri Lanka James Dauris said: “We understand that some British citizens were caught in the blasts but we are unable to say how many people are, or might have been, affected.”
Foreign secretary Jeremy Hunt said he was shocked by the attacks.
He tweeted: “I’m deeply shocked and saddened by the horrifying attacks on churches and hotels in Sri Lanka today.
“To target those gathered for worship on Easter Sunday is particularly wicked.
“My prayers are with the victims and their families, and with those assisting in the response.”
According to local media, 283 people were admitted to hospitals for treatment.
Former England cricket captain Michael Vaughan said his thoughts were with “everyone affected by the awful attacks in Sri Lanka”.
“Such a wonderful country with great people,” he tweeted.
The Prime Minister of Sri Lanka, Ranil Wickremesinghe, also reacted to the news on Twitter.
“I strongly condemn the cowardly attacks on our people today. I call upon all Sri Lankans during this tragic time to remain united and strong. Please avoid propagating unverified reports and speculation.
“The government is taking immediate steps to contain this situation,” he wrote.
Karu Jayasuriya, the Speaker of Parliament in Sri Lanka, blasted the ‘cowardly’ attacks.
“Multiple cowardly attacks this morning were not against any religion or ethnic group, but the whole Sri Lankan nation, bound together by friendship and brotherhood. In this difficult time, let us stand stronger to wipe out these heinous forces from our country, whoever they are,” he wrote.
Alex Agieleson, who was near the shrine, said buildings shook with the blast, and that a number of injured people were carried away in ambulances.
Local TV showed damage at the Cinnamon Grand, Shangri-La and Kingsbury hotels.
Other blasts were reported at St Sebastian’s Church in Negombo, a majority Catholic town north of Colombo, and at Zion Church in the eastern town of Batticaloa.
St Sebastian’s appealed for help on its Facebook page.
The explosion ripped off the roof and knocked out doors and windows at St Sebastian’s, where people carried the wounded away from blood-stained pews, local TV footage showed.
Sri Lankan security officials said they were investigating. Police immediately sealed off the areas.
A seventh explosion was reported in Dehiwela, near Sri Lanka’s capital, on Sunday, Reuters reports.
Prime Minister Theresa May said: “The acts of violence against churches and hotels in Sri Lanka are truly appalling, and my deepest sympathies go out to all of those affected at this tragic time.
“We must stand together to make sure that no one should ever have to practise their faith in fear.”