Sri Lanka suicide bombers pledged allegiance to IS before killing 321 civilians

The Islamic State group released a video of the Sri Lanka suicide bombers pledging allegiance to the extremist group on Tuesday, hours after an affiliated news agency claimed the attack.

In the video, the attackers join hands and pledge allegiance to IS leader Abu Bakr al-Baghdadi.

The extremist group earlier on Tuesday claimed responsibility for the devastating series of suicide bomb attacks which hit hotels and churches, where worshippers were attending Easter Mass, in Sri Lanka.

The death toll for the attacks on Tuesday rose to 321 people, at least 45 of whom were children.

In a later statement published by IS propaganda agency Amaq, IS identified the attackers by their noms de guerre. They also explained that the attacks had targeted "crusader" Christians and citizens from countries involved in the US-led coalition defeat of the so-called "caliphate" in Syria and Iraq.

Both the statements and video released by Amaq have raised questions over why IS waited so long to claim the attacks.

The Sri Lankan government said on Monday that it believes the National Thowheeth Jama'ath (NTJ), a local jihadi group, carried out the series of deadly suicide attacks, but that it had done so with "international support".

"We don't see that only a small organisation in this country can do all that," government spokesman Rajitha Senaratne said.

"We are now investigating the international support for them, and their other links, how they produced the suicide bombers here, and how they produced bombs like this."

The purported leader of the attacks, alternately known as Mohammed Zahran or Zahran Hashmi, had been publishing videos online calling for non-Muslims to be killed, according to Sri Lankan Muslim community leaders.

Sri Lanka also announced on Tuesday that investigators believe the attacks were carried out in "retaliation" for last month's attacks on two mosques in Christchurch, New Zealand.

Fifty people were killed when a right-wing extremist entered two mosques in the New Zealand city of Christchurch on 15 March, shooting worshippers as they took part in the weekly Friday prayers.

Neither of IS' statements mentioned the Christchurch attacks.

Sri Lankan President Maithripala Sirisena responded on Tuesday by saying he would replace the heads of the country's defence forces for failing to prevent the attacks despite having been given prior information about the attacks.

"I will completely restructure the police and security forces in the coming weeks. I expect to change the heads of defense establishments within next 24 hours," Sirisena said in a televised address, according to Reuters.

"The security officials who got the intelligence report from a foreign nation did not share it with me. Appropriate actions would have been taken. I have decided to take stern action against these officials."