Five Indians have been confirmed killed in the string of near-coordinated blasts that ripped through churches and hotels in Sri Lanka, the government has said.

Indian External Affairs Minister Sushma Swaraj said on Sunday that three Indians were killed, and on Monday morning the Indian High Commission in Colombo identified two more persons who perished in the blasts, our New Delhi correspondent reports.

The name of a sixth victim PS Razeena, a woman of Indian origin from Kerala who was settled in Dubai, was given out by Kerala Chief Minister Pinarayi Vijayan.

Prime Minister Narendra Modi spoke to Sri Lankan President Mathipala Sirisena and Prime Minister Ranil Wickramasinge on Sunday, expressing condolence over the loss of so many lives in a string of terror attacks on churches and hotels in that country and termed the incidents as "cold-blooded and pre-planned barbaric acts".

Modi also offered all possible help for ensuring security following the blasts. Five Indians and an Indian-origin woman settled in Dubai were among 215 people killed in the serial blasts in Colombo that ripped through three churches during Easter services, four luxury hotels, where dozens of tourists were staying and a housing complex.

Indian External Affairs Minister Sushma Swaraj tweeted that she spoke to her Sri Lankan counterpart Tilak Marapana and conveyed to him that India is ready to provide all humanitarian assistance and if required, to despatch Indian medical teams as well."

"Prime Minister Modi condemned in the strongest terms the serial terrorist attacks, perpetrated at sites including religious places and during a religious festival. Terming them as cold-blooded and pre-planned barbaric acts, he pointed out that these attacks were another grim reminder of the most serious challenge posed to the entire humanity by terrorism in our region and the entire world," the PMO said in a statement.

Modi "renewed the offer of all possible help and assistance to Sri Lanka for ensuring its security against the challenges such as those posed by terrorism," it said adding Modi also wished the injured speedy recovery and offered all required assistance for their treatment.