Filipino Islamic militants were likely behind an attack on a Vietnamese cargo ship in which one crew member was killed and six others abducted, Philippine Foreign Secretary Perfecto Yasay said Tuesday.
The MV Giang Hai was hit by unknown gunmen Sunday near the southernmost Philippine island of Baguan near the Malaysian coast, in a region notorious for such assaults.
"We can only assume that they were taken by Abu Sayyaf people but this has to be verified," Yasay told a news conference aired live on television, but added that it was "likely".
The waters between Malaysia and the southern Philippines have become increasingly dangerous in recent years as Filipino Muslim extremists have taken to piracy, boarding ships and seizing seamen for ransom.
Maritime officials have warned of an emerging "Somalia-type" situation in the waters if the attacks are not addressed.
Prior to the latest incident the military said the Abu Sayyaf -- one of the armed Islamic groups in the area who have pledged allegiance to Islamic State fighters in Iraq and Syria -- were holding 27 hostages.
They include Filipino, Malaysian, Indonesian, Vietnamese and German hostages, as well as a Dutchman abducted in 2012, according to the military.
Yasay said Vietnam's foreign minister raised the issue at an informal ASEAN ministerial retreat in the Philippines this week.
At least six Vietnamese crew members of another vessel had been abducted in the area in November last year, Yasay said.
The Philippines is planning to ask its defence ally the United States to hold joint exercises in the southern waters, Philippine Defence Secretary Delfin Lorenzana said earlier this month, while President Rodrigo Duterte has also urged China to launch patrols off the piracy-plagued waters.
The International Maritime Bureau said in January the number of maritime kidnappings hit a 10-year high in 2016, with waters off the southern Philippines becoming increasingly dangerous.