British Prime Minister Theresa May Sunday condemned the "truly appalling" multiple blasts at churches and hotels in Sri Lanka on Easter, killing over 160 people, including at least nine foreigners.

Six near-simultaneous and coordinated explosions rocked three churches and three five-star hotels frequented by tourists as the Easter Sunday mass were in progress.

"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," prime minister May said in a statement on Twitter.

"We must stand together to make sure that no one should ever have to practise their faith in fear," she said.

The statement came soon after she called for the UK to stand up for religious freedom in her annual message to mark Easter.

No group has claimed responsibility for Sunday's attacks.

However, most of the deadly attacks in the past in Sri Lanka were carried out by the Liberation Tigers of Tamil Eelam (LTTE) which ran a military campaign for a separate Tamil homeland in the northern and eastern provinces of the island nation for nearly 30 years before its collapse in 2009 after the Sri Lankan Army killed its supreme leader Velupillai Prabhakaran.

No group has claimed responsibility for Sunday's attacks.

However, most of the deadly attacks in the past in Sri Lanka were carried out by the Liberation Tigers of Tamil Eelam (LTTE) which ran a military campaign for a separate Tamil homeland in the northern and eastern provinces of the island nation for nearly 30 years before its collapse in 2009 after the Sri Lankan Army killed its supreme leader Velupillai Prabhakaran.