The mother of Shaini, 13, who died as bomb blasts ripped through churches and luxury hotels on Easter, mourns at her wake, in Negombo, Sri Lanka. Picture: Athit Perawongmetha/Reuters

Colombo - Police have arrested at least 24 people in connection to a series of explosions in Sri Lanka which left at least 290 people dead as investigators confirmed six of the attacks were carried out by suicide bombers, officials said on Monday.

Government Analyst N Welianga told reporters three attacks on churches and three others on the hotels in the capital were carried out by suicide bombers.

The Government Analyst's Department under the Defence Ministry was further probing whether two bombers were involved in one of the hotel attacks, which would mean seven suicide bombers were involved.

Police spokesman Ruwan Gunasekara said that the individuals arrested, all locals, were being questioned by the Criminal Investigation Department.

The death toll increased overnight as more victims died in hospital and several other bodies were discovered.

A dusk-to-dawn curfew imposed throughout the Indian Ocean island nation was lifted on Monday morning. Schools and universities are expected to remain shut while the stock exchange has suspended trading until further notice.

Authorities have so far located a van believed to have transported the bombers and the house where they stayed in the outskirts of the capital Colombo.

Late on Sunday night, a home-made bomb was found inside a plastic pipe close to the airport and defused, a spokesman for the Air Force said.

There has been no claim of responsibility for the multiple explosions. Prime Minister Ranil Wickremesinghe said he would seek support from abroad to find out whether the attackers were linked to international terrorism.

The explosions took place during busy Easter services at Christian churches in the cities of Negombo, Batticaloa and Colombo and in three five star hotels in the capital.

At least 35 foreigners are among those killed, while 19 more remain in hospital.