Abdul Lathief Jameel Mohamed, 36, blew himself up in guesthouse while trying to fix suicide device after botched hotel attack

Sri Lanka’s prime minister says investigators of Easter Sunday’s deadly string of suicide bombings are aware of “some militancy going on in Australia” and believe one of the attackers may have been radicalised while studying in the country.

Ranil Wickremesinghe told Guardian Australia that Abdul Lathief Jameel Mohamed, who undertook a postgraduate degree at Melbourne’s Swinburne University in 2009 and left the country in 2013, appeared to have been influenced by extremist ideas during that period.

“That’s how the family feel,” Wickremesinghe said at his prime ministerial residence in Colombo. “We know there is some militancy going on in Australia among the Muslims. Australia has been out there fighting [in the war on terror].”

Wickremesinghe confirmed Mohamed, who also studied in the UK, had intended to detonate a bomb in the luxury Taj Samudra hotel, located between the Cinnamon Grand and Shangri-La hotels that were struck on Sunday.

Sri Lanka: at least 15 killed as police raid suspected bomber hideout Read more

But the explosives failed to detonate and he retreated to a guesthouse where he had been staying in the neighbourhood of Dehiwala. As he tried to repair the bomb, it accidentally went off, killing him and two others, Wickremesinghe said. “He was trying to fix it and the whole thing exploded.”

Samsul Hidaya, Mohamed’s sister, said in an interview earlier in the week that her brother had returned from Australia “a different man”.

“He had a long beard and had lost his sense of humour,” Hidaya told the Daily Mail. “He became serious and withdrawn and would not even smile at anyone he didn’t know, let alone laugh.”

Hidaya said she would frequently argue with her brother about religion. “At first he started quoting scripture and I would say OK, you’re right,” she said.

“But then the conversation got deeper and deeper into religion and I couldn’t follow what he was saying any longer.

“He told male relatives off for trimming their beards and became angry and totally crazy,” she said. “So I just stopped speaking to him because it got to the point where it was getting out of hand.”

The Australian reported on Friday that Mohamed, 36, had previously been one of the subjects of a terrorism investigation by Australian police based on evidence linking him to the Islamic State recruiter Neil Prakash.

The pair is not believed ever to have met but there was at the minimum an online link between them, the report said.

Prakash, 27, was a prominent figure in Isis propaganda videos in which he urged Muslims to travel to Syria and Iraq to join the purported caliphate. Prakash’s Australian citizenship was revoked in December. He is in a Turkish prison and has been charged with terrorism offences.

Wickremesinghe said authorities were investigating the possibility that the terrorist cell responsible for the Easter Sunday attacks may have expected a second wave of people to come forward to become suicide bombers.

Sri Lanka PM: terrorists may have expected second wave of bombings Read more

He said investigators were trying to understand why the Isis-linked terrorist cell that killed at least 253 people had such a large quantity of explosives they were yet to use, some of which had been dumped in safe houses across the country. “Were they keeping [the explosives] for numbers to build up? Maybe this [the Easter Sunday attacks] would spark off other people joining the cause. There would have been people to give them explosives,” he said.

The hunt for accomplices of the nine suicide bombers continued on Saturday. The bodies of 15 people, including six children, were discovered after a fierce overnight gun battle on the east coast of Sri Lanka, a military spokesman said on Saturday. Authorities said another four gunmen and a civilian were killed in the shootout.

The shooting between troops and suspected Islamist militants erupted on Friday evening in Sainthamaruthu in Ampara, to the south of the town of Batticaloa, site of one of the Easter Sunday blasts at luxury hotels and churches.

Gunmen opened fire on troops when they attempted to storm a house, military spokesman Sumith Atapattu said. “In our retaliatory fire two gunmen were killed,” he said adding that a civilian caught in the crossfire was also killed.

Police later said clearing operations on Saturday showed four suspected suicide bombers among the dead.

