Authorities were aware of "a small group" of Lankans who travelled abroad to receive training from ISIS

Highlights Foreign mastermind may have planned Easter Sunday blasts, says President

Investigations revealed bombs used in Easter attacks were made locally

Security forces in Sri Lanka have been ordered to remain on high alert

Sri Lankan President Maithripala Sirisena said a foreign mastermind may have planned the Easter Sunday bombings, claimed by Islamic State, telling the terrorist group to "leave my country alone".

Sirisena also warned it may be possible Islamic State had launched a "new strategy" by targeting smaller countries, Sky New said on Wednesday.

A government source told news agency Reuters on Tuesday police and other security forces across the Buddhist-majority country had been ordered to remain on high alert because the terrorists were expected to try to strike again, before the holy month of Ramadan which starts on Monday.

Sirisena said authorities were aware of "a small group" of Sri Lankans who had travelled abroad to receive training from Islamic State over the past decade.

Investigations revealed the bombs used in the Easter attacks were made locally, the president said in the interview.

The suicide bombings on hotels and churches killed more than 250 people, including 40 foreign nationals.

Police suspect members of two previously little-known groups - National Thawheedh Jamaath and Jammiyathul Millathu Ibrahim - of carrying out the attacks.

On Monday, Islamic State's media network published a video message purporting to come from its leader, Abu Bakr al-Baghdadi, which would be his first appearance since declaring the jihadists' now-defunct "caliphate" five years ago.

In the video, a bearded man with Baghdadi's appearance says the Sri Lanka bombings were Islamic State's response to losses in its last territorial stronghold of Baghouz in Syria.

In the Sky News interview, Sirisena said he had a message for Islamic State: "Leave my country alone."

Sri Lankan authorities have previously said that they suspect the attackers had international links, although the precise nature of those connections aren't known. The U.S. Federal Bureau of Investigation and Interpol, as well as other undisclosed foreign agencies, are helping Sri Lanka with the probe.

Local intelligence officials believe that Zahran Hashim, a Tamil-speaking preacher from the east of the Indian Ocean island country, may have been a key player in plotting the Easter bombings. Officials believe he was one of nine suicide bombers.