Colombo, April 25 (IANS) Some of the suspected attackers responsible for the Easter Sunday bombings in Sri Lanka were being monitored by the countrys intelligence services, Prime Minister Ranil Wickremesinghe told CNN in an interview on Thursday.

But there was not "sufficient" evidence to put the suspected attackers in custody prior to the attacks, Wickremesinghe said.

He reiterated that the attackers were middle- and upper-middle class and had been educated abroad. He added that the profile of the suspected bombers was "surprising".

A string of suicide bombings in Sri Lanka on Easter Sunday killed 359 people and injured hundreds. The Islamic State claimed responsibility but Sri Lankan authorities have blamed a local Muslim group for the carnage.