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 and the president had also declared April 23 a National Day of Mourning.

The death toll from the multiple explosions which shook Sri Lanka on Sunday has risen to 290, while over 500 have been injured, the police said Monday.

Earlier reports put the number of casualties at 228, with 450 wounded in the nine attacks that occurred across the country on Sunday.

The Sri Lanka Tourism Development Authority said Sunday evening in a statement that 32 foreigners were among those killed.

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 a local radical group the National Towheed Jamaat was responsible for the attacks and investigations were ongoing to find out whether 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 added.

President Sirisena, quoted by local media, 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 8:00 p.m. Monday to 4:00 a.m. local time Tuesday in order to maintain law and order.

The curfew imposed after the deadly attacks had been lifted on Monday morning.

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

Police Spokesperson SP Ruwan Gunasekara said 24 suspects had been arrested so far and investigations were ongoing to nab more suspects.

Two of the suspects arrested were nabbed from Dambulla in the Central Province on Monday morning, the spokesperson said.

Sri Lankan Prime Minister Ranil Wickremesinghe said all arrested were local citizens.

President Sirisena, who was abroad when the attacks happened, called a meeting of the National Security Council early on Monday.

Police investigation into the bombings will examine reports that the intelligence community failed to detect or warn of possible suicide attacks before the violence, according to local media.

Another minor explosion was reported here on Monday as Sri Lanka's Bomb Disposal Unit defused a bomb which was found in an abandoned vehicle, local media reported.

The vehicle was parked 50 meters away from the St. Anthony's Church in Kochchikade, where one of the multiple deadly attacks took place on Sunday.

Local media quoted the police as saying that the Bomb Disposal Unit defused the bomb in a controlled explosion. No injuries were reported.

Meanwhile, police said it discovered 87 low explosive detonators abandoned at Colombo's main public bus station in the business hub of Pettah.

The explosives were found at the bus stand in Bastian Road when police were conducting search operations, police spokesperson Ruwan Gunasekara said.

Sri Lankan tri-forces, together with the police, have launched massive search operations since nine explosions rocked the country on Sunday, targeting churches and high-end hotels.

On Sunday evening, the Sri Lanka Airforce successfully detonated a bomb which was planted close to the Bandaranaike International Airport.

Schools remained closed on Monday and will also close on Tuesday.

Security had been beefed up across the country and tight security would remain in place, the police said.

The wave of attacks started Sunday morning as explosions were reported from the St. Anthony's Church in Kochchikade in capital Colombo and another from the St. Sebastians Church in Negombo, on the outskirts of the capital.

A third explosion was reported from the Zion Church in Batticaloa, in the east.

Explosions were also reported from three star-class hotels in Colombo while on Sunday afternoon an explosion was reported from a hotel, opposite the zoo in Dehiwala, in Colombo and another from a housing complex in Dematagoda, in Colombo.

The attacks marked the most deadly violence in Sri Lanka since a bloody civil war ended 10 years ago.