A Singaporean militant was killed in clashes last month that intelligence officials here believe may have led to a deadly bombing in the war-torn southern Philippine island of Mindanao.
A senior military official has identified the man as Abu Hud Zain, a Singaporean. It was not clear whether this was his real name or an alias.
Investigators have yet to recover his passport or any documents to confirm his identity, according to the official, who asked not to be named because of the nature of the information he was sharing.
The Ministry of Home Affairs said Singapore is in touch with the Philippine authorities to gather more information on the individual.
Zain was killed in covert operations by security forces in Mamasapano town, Maguindanao province, on Dec 22.
Also killed were an Indonesian, Abdulrahid Ruhmisanti, and brothers Salamuddin and Mohammad Hassan, both Filipinos.
This happened about a week before a bomb went off in front of a mall in Cotabato city on Monday, killing two and wounding dozens.
Major-General Cirilito Sobejana, chief of the 6th Infantry Division, told reporters that the attack was probably in retaliation for the deaths of the four militants.
It is believed Zain was part of the Muhajireen Wal-Ansar, also known as the Maguindanao Daulah Islamiyah. It is a faction of the Bangsamoro Islamic Freedom Fighters (Biff) under the firebrand preacher Esmael Abdulmalik, also known as Abu Turaife.
Biff is a splinter group of the 12,000-strong Moro Islamic Liberation Front (MILF), the main secessionist group that has been holding peace talks with the government.
Intelligence officials said the Turaife group, consisting of about 150 militants, had been roaming a sprawling marshland from North Cotabato province to Maguindanao.
It has been providing shelter to fighters for the Islamic State in Iraq and Syria (ISIS) across South-east Asia, the Middle East and North Africa, they said.
Zain was the second Singaporean extremist known to be fighting in the Philippines, after Abdullah Ali, alias Muawiyah, whose fate is unknown. Zain's death highlights the presence of foreign terrorists in the battlegrounds of the southern Philippines, an issue that worries regional governments as Indonesians and Malaysians are known to be involved. A major security concern is that these militants would one day bring their battlefield experience home to sow chaos.
Over a thousand militants aligned with ISIS stormed and laid siege to the southern Islamic city of Marawi in May 2017, sparking five months of intense fighting and military airstrikes that left more than 1,100 people - mostly militants - dead and displaced hundreds of thousands of villagers.
Philippine security officials have said remnants of the militant groups behind the siege have fled to remote areas where Biff has been operating freely.
Maj-Gen Sobejana said the bombing in Cotabato could also be intended to derail a plebiscite set for this month to ratify a long-awaited law to allow minority Muslims in Mindanao to start moving towards self-rule by 2022.
The Bangsamoro Organic Law is the culmination of a lengthy and rocky peace accord with the MILF. But the militants are opposed to it, insisting instead on carving out an ISIS "province" in Mindanao.
"There is a strong indication that the attack is, in a way, political in nature," said Ms Sidney Jones, director of the Jakarta-based Institute for Policy Analysis of Conflict, and an expert on terrorism in South-east Asia.
But Ms Jones believes the blast may have been meant to send a message to the Sayadi family, who are in power in Cotabato city.
Mayor Cynthia Guiani-Sayadi has predicted that Cotabato city will likely reject the Bangsamoro law.