A foreign mastermind may have been behind the Easter Sunday bombings in Sri Lanka, the president said on Wednesday, as he told Islamic State to leave his country alone.

President Maithripala Sirisena warned in an interview that the attacks against churches and hotels in which more than 250 people died could signal a "new strategy" by IS to hit smaller countries that make softer targets than more powerful nations.

He said there are clear links between the attackers and IS, possibly including training.

Asked whether there could be a foreign mastermind, the president said: "That is quite possible, given the phone calls they were making and the fact that some of them had received training abroad, and the fact that IS leaders have already made statements... admitting links to Sri Lanka - that is something we can assume."

CCTV footage has emerged showing some of the eight suicide bombers on 21 April using their mobile phones as they prepared to hit their targets.


Image: President Maithripala Sirisena told Sky News there is 'clear evidence' IS was behind the attack

President Sirisena said: "It is quite possible they were getting in touch with the people abroad who were helping them.

"It is also quite possible they were getting in touch with the rest of their group in Sri Lanka. The two assumptions we've made so far."

Islamic State has said it was behind the killings, posting a video last week of eight suspects pledging allegiance to Abu Bakr al Baghdadi, the IS leader.

Who were the Sri Lanka suicide bombers? Full report

The one man in the video whose face is not covered by a scarf was Mohamed Hashim Mohamed Zahran, a self-styled radical preacher from eastern Sri Lanka.

He is the suspected ringleader of the group and is believed to have killed himself in a bomb blast at the Shangri-La hotel.

I asked the president whether he thought the Sri Lanka attacks signalled new campaign by the terrorist groups to launch attacks around the world.

Image: Sri Lanka's president spoke to Sky's Deborah Haynes

He said: "When IS was at height of their power... they targeted the most powerful countries in the world, from the EU to the UK to Indonesia. They attacked a large number of countries, including Australia and other countries.

"At that time - smaller countries were not really their target. Right now I'm left with the question as to why they targeted Sri Lanka. It is possible they have launched a new plan, a new strategy - like you suggested."

On Monday, the IS leader made his first comments on camera for five years. He signalled the Sri Lanka attacks were in response to the loss of the final piece of IS territory in Syria.

Bomber pictured before church attack

The president had a message for al Baghdadi: "Sri Lanka is a free and peaceful country... Clearly we haven't had any clashes with IS until now, until they launched this attack against us. Therefore my request to this person would be to leave my country alone."

Sri Lankan investigators, with help from other countries, are looking into the international connections to the bomber group, including one attacker who studied in the UK.

The president said he had not seen any indication that Abdul Latief Jameel Mohammed - at Kingston University between 2006 and 2007 - had been radicalised during his time in Britain.

As well as the suspected foreign involvement, the bombers had their own deadly skills.

The president told Sky News that the explosives they used to kill and maim worshippers, tourists and others were made in Sri Lanka - a country that is no stranger to conflict after almost three decades of civil war that only ended with the defeat of the Tamil Tigers in 2009.

Sri Lanka's leader is under pressure after it emerged a number of specific advanced warnings about the bomb plot received by his security chiefs were not properly acted upon.

Image: Abu Bakr al Baghdadi is the leader of IS and said that they were behind the Sri Lanka attack

However, the president said he has no plans to resign even though the attacks happened on his watch. He noted that George W Bush did not step down as president after the 11 September 2001 attacks on the US, instead taking action to tackle the threat.

He added: "That is what I intend to do. People of my country have not demanded resignation - they want me to secure safety and security.

"Resigning at a time like this would be act of cowardice. I will not resort to acts of cowardice."

A number of governments around the world, including the UK, has warned their citizens not to travel to Sri Lanka - a hugely popular tourist destination - at this time of heightened threat.

President Sirisena indicated he did not think such a warning was warranted: "Tourists can come to Sri Lanka, even now. We are in a position to provide them the security they need."