A wave of bombings that killed 290 people in Sri Lanka on Sunday was carried out with the support of an international network, officials say.

The government blamed a previously unknown local jihadist group, National Towheed Jamath, for the attacks, but said it had help from abroad.

Another 500 people were injured in the suicide attacks on churches and hotels.

A nationwide emergency will be declared from midnight on Monday, the president's office has said.

Police have arrested 24 people in a series of raids.

Sri Lankan authorities were warned two weeks before the Easter Sunday attacks, and had the names of suspects, a cabinet spokesman has said, as the death toll from the string of bombings rose to 290, with about 500 injured.

“Fourteen days before these incidents occurred, we had been informed about these incidents,” Rajitha Senaratne told a press conference in the capital, Colombo, on Monday.

“On 9 April, the chief of national intelligence wrote a letter and in this letter many of the names of the members of the terrorist organisation were written down.”

Senaratne said the intelligence memo warning about the attacks had named the radical islamist group National Thowheeth Jama’ath as the perpetrators. National Thowheeth Jama’ath is a newly formed radical islamist group in Sri Lanka who are strong proponents of the global jihadist movement. They are known for being a virulently anti-Buddhist and have been linked to the vandalisation of Buddhist statues, with four of their members arrested in January.