Mohammad Zahran Hashim — the suspected mastermind of the Sri Lankan Easter bombings — spent a "substantial amount of time in south India", The Hindu reported on Friday citing a top source within the Sri Lankan military.

“We are looking into the IS angle. We also suspect that some of those radical youth (suspected bombers) were indoctrinated and trained in India, possibly Tamil Nadu,” revealed the senior military official, who wished to remain anonymous.

While Indian officials did not state that Hashim had travelled to India, they did point out that he had maintained virtual links with youth believed to be of Indian origin, said The Hindu.

Hashim's ties with south India were also confirmed by Hilmy Ahamed, vice-president of the Muslim Council of Sri Lanka.

"Hashim had shifted base to southern India," he told AFP, adding that "all his videos have been uploaded from India. He uses boats of smugglers to travel back and forth from southern India."

The militant Islamic State group had claimed responsibility for the terror attacks that left more than 250 dead, and also released a picture showing eight suspected bombers. Among them, the only man seen with his face uncovered is believed to be Hashim.

Hashim was identified by investigators as the leader of the National Thowheed Jamaath, the group believed to have executed the highly coordinated series of explosions last Sunday that saw over 250 people killed. However, it later appeared that he may have broken off from the NTJ and founded another extremist outfit that assisted with the attacks.

Meanwhile, more than a hundred of Hashim's Facebook followers are being scrutinised, said an official on condition of anonymity.

The notion that Hashim made use of "doctrinal videos" in order to likely radicalise youth, first emerged when Indian authorities questioned seven individuals of a group whose leader was found to be a follower of Hashim.

"The men were IS sympathisers and arrested in September 2018 in Coimbatore, on suspicion that they were plotting the assassination of certain political and religious leaders in India," The Hindu said, quoting the official.

Hashim carried out Shangri-La bombing

Although Sri Lankan authorities have yet to officially name any of the nine suicide bombers or suspects, officials confirmed on Friday that Hashim was one of two bombers who executed the blasts at the Shangri-La Hotel in Colombo.

"He led the radical group in (the town of) Kattankudy, in Batticaloa district of Sri Lanka’s Eastern Province, and was known for espousing extremist religious ideas, often to the discomfort of many within the community," The Hindu reported.

Locals also told the publication earlier this week that two years ago, Zahran had left the town, after a "fierce disagreement" with the local religious scholar regarding the practice of Islam.

He had since then remained absconding, community leaders told The Hindu.