Sri Lanka's army chief says other groups of Islamic extremists could be operating in the country independent of the one that carried out Easter Sunday bomb attacks.

Lt. Gen. Mahesh Senanayake said Thursday that "There could be other groups, definitely."

He said the army is investigating the possible groups.

More than 250 people were killed in coordinated suicide bomb attacks at three churches and three hotels on Easter Sunday that were claimed by the Islamic State group and carried out by a local radicalized Muslim group.

Senanayake said the military is developing a two-year plan to eliminate the new terrorist threat.