Security is still tight in Colombo after the Easter Sunday attacks

The Sri Lankan Prime Minister, Ranil Wickremesinghe, has warned of the potential for more attacks in the country. In an interview with CNN's Ivan Watson, he said authorities were targeting "sleepers" -- terrorists who could activate to initiate another round of attacks.

"Police and security forces are rounding up those involved, but they're also rounding up the sleepers, those used on second and third rounds (of attacks)," he said.

"The danger has come down drastically, (but) we do have to pick up some more sleepers, which we will do in the next few days."

He said that security services were acting out of an abundance of caution, and that should even one militant slip through the net, the damage could be widespread. "It is a precaution that we are taking, we want to be sure we have everyone in," he said in the interview.

"They are worried that one or two could get into a church -- (even) one person can do a lot of damage."

The Archdiocese of Colombo has suspended all Catholic church services until April 29 because of security concerns,.