Sri Lankan President Maithripala Sirisena said on Friday police are looking for 140 people believed to have links with the Islamic State group over the Easter Sunday attacks on churches and hotels that killed at least 253 people.

Sirisena told reporters some Sri Lankan youths had been involved with the extremist group since 2013, and that top defence and police chiefs had not shared information with him about the impending attacks.

He also blamed Prime Minister Ranil Wickremesinghe's government for weakening the intelligence system by focusing on the prosecution of military officers over alleged war crimes during a decade-long civil war with Tamil separatists.