COLOMBO, April 22 (Xinhua) -- Sri Lankan President Maithripala Sirisena's office said on Monday that a conditional state of emergency would be declared in the island country from midnight Monday following the deadly blasts on Easter Sunday.

A statement released by the President's Media Division (PMD) said the decision was taken to ensure the safety of citizens.

The PMD said that the president had also declared April 23 a National Day of Mourning, as the death toll from the eight explosions which occurred on Sunday had risen to 290. Over 500 have been injured.

Sri Lanka's security forces have launched massive search operations to arrest all those involved and the police said so far 24 suspects had been arrested.

Sri Lanka's Health Minister Rajitha Senaratne said that a local radical group - the National Towheed Jamaat - was responsible for the attacks and investigations were ongoing to try to find out if they had foreign links.

"We do not believe these attacks were carried out by a group of people who were confined to this country," Senaratne said.

President Sirisena, quoted by local media reports, said he would seek the assistance of the international community to conduct investigations into the attacks.

Meanwhile, the police said an islandwide curfew would be re-imposed from 8 p.m. Monday to 4 a.m. local time Tuesday in order to maintain law and order in the country.

The police have urged people to remain indoors and prevent gathering in public places.