JAKARTA • Indonesia is investigating reports from supporters of the Islamic State in Iraq and Syria (ISIS) that the most senior South-east Asian commander of the militant group was killed by US air strikes in eastern Syria last week, counter-terrorism officials said.

Online messages from ISIS propagandists viewed by Reuters said that Bahrumsyah, an Indonesian national, died after United States air strikes hit Hajin, north of the Syrian city of Abu Kamal, on Tuesday last week.

A spokesman for Indonesia's Foreign Ministry, Mr Arrmanatha Nasir, said the embassy in Syria had made inquiries but had yet to confirm Bahrumsyah's death.

Two senior Indonesian counter-terrorism officials, speaking on condition of anonymity, said they were taking the online reports seriously.

"We are in the process of investigating," said one senior official.

If the reports were true, the death would become a "motivation to carry out reprisal attacks" in Indonesia, the senior official said.

Pentagon spokesman Eric Pahon said US aircraft were bombing the "general area" in eastern Syria on the day Bahrumsyah was believed to have died but was unable to confirm his death.

Besides leading Katibah Nusantara, an armed unit comprising more than 100 South-east Asians, Bahrumsyah also organised funding for the militant rebels who captured part of the southern Philippines city of Marawi in a bloody siege last year, analysts and officials said.

A message purportedly from ISIS figure Abu Nuh, reviewed by Reuters, said Bahrumsyah had been attending a meeting of leaders when he was killed.

There were reports last year of Bahrumsyah's death, but analyst Sidney Jones from the Jakarta-based Institute for Policy Analysis of Conflict said that the latest report had a "much higher degree of credibility".

"As far as we know, he was the highest-ranking Indonesian to fight with ISIS," said Ms Jones.

His death, if confirmed, would be a blow to pro-ISIS forces in South-east Asia, where fears of hardened fighters returning from Syria have the authorities on alert.

More than 600 Indonesians, including at least 166 women and children, have travelled to Syria to join ISIS, according to data from the counter-terrorism agency in Indonesia, reviewed by Reuters.

REUTERS