The suspected leader of the militant group Sri Lankan authorities say carried out a series of Easter Sunday bombings died in the attacks.

Police said on an official Twitter account that Mohamed Zahran, the leader of local militant group National Towheed Jamaat known for his vitriolic extremist speeches on social media, had been killed in one of the nine suicide bombings.

Police also said they had arrested the group’s second-in-command.

They said investigators had determined that the assailants’ military training was provided by someone they called “Army Mohideen”, and that weapons training had taken place overseas and at some locations in Sri Lanka’s Eastern Province.

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Sri Lankan security officers inspect a suspicious vehicle parked near St Anthony’s shrine (Eranga Jayawardena/AP)

Police also said that the attackers had worked out at a local gym and by playing football using their authentic national identity cards.

They added that the vehicles used in the attack were purchased from a car dealership in Kadawatha, a suburb of the capital Colombo.

They said that the operator of a copper factory who was arrested in connection with the bombings had helped Mohideen make improvised explosive devices and purchase empty cartridges sold by the Sri Lankan military as scrap copper.

Australia’s prime minister said earlier on Friday it had been confirmed that the Sri Lanka attackers were supported by the Islamic State group, which has claimed responsibility for the massacre, distributing video of Zahran and others pledging allegiance to the caliphate.

Sri Lankan President Maithripala Sirisena told reporters in Colombo that some 140 people in the island nation had been identified as having links to the Islamic State group, and that the Sri Lankan government has “the capability “to completely control Isis activities” in the country.

“We will completely control this and create a free and peaceful environment for people to live,” he said.

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People gather around a television in a cafe showing Sri Lankan President Maithripala Sirisena’s address to the nation (Gemunu Amarasinghe/AP)

Mr Sirisena blamed Sri Lanka’s defence secretary, who resigned Thursday, and police chief, who he said would soon step down, for a failure to share weeks of information from international intelligence agencies about the plot ahead of time.

Across Colombo on Friday, there was a visible increase of security as authorities warned of another attack and pursued suspects that could have access to explosives.

Armed soldiers stood guard outside St Anthony’s Shrine, one of the three churches attacked, and nearby shops were closed.

Authorities told Muslims to pray at home rather than attend communal Friday prayers that are the most important of the week.

In an interview on Thursday with The Associated Press, Prime Minister Ranil Wickremesinghe said he feared some of the suspects “may go out for a suicide attack”.

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Sri Lankan prime minister Ranil Wickremesinghe (Eranga Jayawardena/AP)

After, in an unusually specific warning, the US Embassy in Sri Lanka said places of worship could be hit by extremists this weekend.

The UK’s foreign ministry advised its citizens not to travel to the island nation off the tip of India.

Late on Thursday, Sri Lanka’s health ministry drastically revised down its estimated death toll from the coordinated attacks.

A statement said “approximately” 253 people had died, nearly one-third lower than the police’s estimated death toll of 359.

The discrepancy was not immediately explained, but it fit a pattern of claims and counterclaims by Sri Lankan officials that have muddled the investigation.