US President Donald Trump Monday telephoned Sri Lankan Prime Minister Ranil Wickremesinghe and pledged support in bringing to justice the perpetrators of the country's worst terror attacks that killed 290 people.

Expressing his condolences over a series of devastating blasts at churches and luxury hotels in Sri Lanka on Easter Sunday which also wounded 500 people, Trump and Wickremesinghe discussed the ways to combat the issue of global terrorism.

Seven suicide bombers believed to be members of an Islamist extremist group carried out a string of blasts that rocked churches and luxury hotels in Sri Lanka, killing 290 people in the country's worst terror attack.

Trump called Wickremesinghe "this morning" to express condolences to the people of Sri Lanka for the Easter day terrorist attacks that killed nearly 300 and wounded hundreds of others, White House said Monday.

"The near simultaneous attacks on Sri Lankan churches and hotels constitute one of the deadliest terrorist events since the September 11, 2001 attacks on the United States," it said.

Wickremesinghe expressed appreciation for the President's concern and updated him on the progress of the investigation into the attacks, it said.

"Trump pledged United States' support to Sri Lanka in bringing the perpetrators to justice, and the leaders re-affirmed their commitment to the fight against global terrorism," said the White House in a readout of the call.

Interestingly, Trump did not call Sri Lankan President Maithripala Sirisena who was criticised by the US during the political turmoil in the island nation last year when the president sacked Wickremesinghe as Prime Minister and replaced him with ex president Rajapaksa.