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A group of domestic Islamic extremists were responsible for the Easter Sunday suicide bombings in Sri Lanka, the country's government has said.

The seven suicide bombers were all Sri Lankan citizens belonging to National Thowfeek Jamath, Health Minister Rajitha Senaratne revealed at a news conference on Monday.

The group is believed to have links with foreign terrorist networks.

Officials said the causes of three later bombings on Sunday are still being investigated.

A total of nine bombings on Sunday killed at least 290 people. About 500 others were wounded in the blasts. Officials said 24 suspects were in custody for questioning.

No group immediately claimed responsibility, but 24 people have been arrested in a series of police raids.

Following the tragedy, Telecommunications Minister Harin Fernando tweeted: "Some intelligence officers were aware of this incidence. Therefore there was a delay in action. Serious action needs to be taken as to why this warning was ignored."

Mano Ganeshan, the minister for national integration, said the security officers within his ministry had been warned by their division about the possibility two suicide bombers would target politicians.

Sri Lankan government forensic crime analyst said Ariyananda Welianga said two people were involved in the attack at the Shangri-La hotel. One bomber each attacked the Cinnamon Grand and Kingsbury hotels, and St Anthony's Shrine in Colombo, St Sebastian's church in the city of Negombo and Zion Church in the city of Batticaloa.

Two bombings hours later at a guesthouse and near an overpass on the outskirts of Colombo are still being investigated. Suspects detonated explosives at a safe house near the overpass blast, killing three officers.

The explosions, mostly in or around the Sri Lankan capital Colombo, collapsed ceilings and blew out windows, killing worshippers and hotel guests.

Most of those killed were Sri Lankans and the country's foreign ministry said the bodies of at least 27 foreigners from countries including Britain, the US, China, Japan, Portugal, Denmark and Australia also died.

The Sri Lankan government lifted a curfew that had been imposed during the night but most social media remained blocked on Monday after officials said they needed to curtail the spread of false information and ease tension in the country.