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Sri Lankan President Maithripala Sirisena said Tuesday that he will fire senior officials who did not heed warnings that a Islamist group was plotting suicide attacks against churches in the country.

"I must be truthful and admit that there were lapses on the part of defense officials," he said. On Easter Sunday, coordinated suicide bombings at churches and hotels left more than 300 people dead and 500 more injured. Sirisena said officials were aware there "was an intelligence report on the attack," but he was "not kept informed."

Sirisena's senior adviser Shiral Lakthilaka announced that two positions are "earmarked for dismissal": secretary of the ministry of defense and inspector general of police. Critics say Sirisena has to take some of the blame, since he wouldn't let Prime Minister Ranil Wickremesinghe, his political rival, attend security meetings.

The Islamic State has claimed responsibility for the attacks, and posted a video online featuring an extremist preacher from Sri Lanka named Mohammed Zaharan. Officials suspect that Zaharan, who led a small group called National Thowfeek Jamaath that defaced Buddhist statues, was the attack's ringleader; his whereabouts are unknown, and officials believe he may have been a suicide bomber, The New York Times reports. Indian officials on Tuesday said they had been keeping an eye on Zaharan, as they suspected he was an online recruiter for ISIS.