(Adds island governor's comments)

MANILA, Feb 4 (Reuters) - At least two soldiers and three Islamic rebels were killed on a remote island in the southern Philippines on Monday, when U.S.-trained troops clashed with militants holding two people hostage, an army spokesman said.

Another rebel group in the area said at least 16 civilians were also killed in the gunbattle, but that figure has yet to be verified.

Abdusakur Tan, the governor of Jolo island, said he had ordered an investigation into the alleged killing of civilians.

"I was told four or more people were killed, but we're still trying to get to the bottom of the incident," Tan told reporters.

Major Eugene Batara said troops were on a mission to rescue two hostages, including the daughter of a wealthy local trader, when they clashed with Abu Sayyaf rebels.

"We lost two men but we killed three on their side," Batara said, adding five soldiers were also wounded in the hour-long gunbattle.

"Our troops recovered an assault rifle and the bodies of three dead rebels. Our wounded have been airlifted to a trauma unit facility in Jolo town."

There was no immediate word on the hostages.

The Moro Islamic Liberation Front (MILF), the biggest rebel group in the country, said 16 residents of a coastal village were also killed.

Mohaqher Iqbal, the MILF's chief peace negotiator, said a group of soldiers in a rubber boat were fired upon before dawn.

"The soldiers returned fire, hitting civilians, including some children," Iqbal told Reuters by phone from the southern region of Mindanao.

Lieutenant-General Nelson Allaga, commander of military forces in the southern Philippines, said they were still investigating.

"I'm afraid there might be some collateral damage," Allaga told reporters, but denied soldiers opened fire indiscriminately.

The Abu Sayyaf, one of the deadliest Muslim militant groups in Southeast Asia, is known for kidnapping-for-ransom and was blamed for the country's worst bomb attack, the sinking of a ferry in 2004 that killed 100 people.

Since 2002, Washington has sent elite military units to help train and advise local soldiers in the south of the archipelago, including on Jolo.

On Feb. 18, about 6,000 U.S. soldiers will hold conventional and anti-terrorism drills with 2,000 Filipino troops during the two-week annual Balikatan (shoulder-to-shoulder) exercises in several areas in the country, including on Jolo. (Reporting by Manny Mogato; Editing by Raju Gopalakrishnan and Alex Richardson)

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