The Philippine Navy recently found a large steel marker bearing Chinese inscriptions and hundreds of yellow buoys in waters near the Reed Bank, an area of the South China Sea where Manila has long explored for oil and gas, Philippine naval sources said.

One source, a sailor, said he was on a fishing boat being used by the navy that discovered the rubber buoys and the floating steel marker at the end of May. The buoys stretched "as far as the eye could see," the sailor said.

He said there was no evidence Chinese ships had placed them near the Reed Bank, which Beijing also claims.