A US drone believed to be used for reconnaissance was recovered on Monday in waters off the central Philippines, police and naval authorities said.

Fishermen found the 3.65 metre (12-foot) drone floating off Masbate island and dragged it to shore, said provincial police chief, Senior Superintendent Heriberto Olitoquit.

They initially thought they had hauled in a bomb and alerted police, Olitoquit said.

"A technical evaluation determined that the object is one unmanned aerial vehicle," Olitoquit told reporters.

Olitoquit said the drone had been turned over to the Philippine Navy, which would conduct a thorough investigation.

"It appears to have been floating for quite some time," Captain Rommel Galang, deputy commander of naval forces in the area, told AFP.

"We will first study this drone but initially it appears to be a UAV used largely in reconnaissance."

He said it had inscriptions and a serial number that "indicate it is an American drone".

Galang said the US embassy had been informed of the discovery and local authorities would eventually turn it over to them.

In an interview with AFP last year, President Benigno Aquino confirmed US drones were allowed to fly across the Philippines for reconnaissance purposes, but were not allowed to conduct strikes.

The Philippines is a close American ally and has long relied on its former colonial ruler for help in dealing with its many security threats. The United States is also the Philippines' biggest supplier of military hardware.

About 600 US forces have been rotating in the southern Philippines since 2002 to help train local troops to deal with Islamic militants.

However, Masbate, where the drone was found, is many hundreds of kilometres (miles) from the Muslim insurgency-wracked southern regions and no US troops are known to operate there.

One major security problem in Masbate is the support there for communists who have been waging a decades-long rebellion that continues to claim dozens of lives every year.

The US embassy in Manila released a statement on Monday saying it was looking into reports of the drone's recovery, without confirming the plane belonged to the United States.

"We are aware of reports that an apparently U.S.-made unmanned aerial vehicle was recovered in the waters off of Masbate this weekend," the statement said.

"The recovered vehicle appears to be of the sort that is used as an air defence target in training exercises. This type of vehicle is not armed and not used for surveillance. We are trying to confirm this interpretation and to determine how and when it may have landed in the sea."

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