North Korea is searching for one of its submarines after losing contact with it, Younhap news agency reported on Saturday.

Three unidentified US officials said that US spy satellites, aircraft and ships have been secretly watching the North's navy searching for the missing submarine for days.

US officials believe the submarine "suffered some type of failure during an exercise," though it's unclear if the vessel is adrift under the sea or if it sank, the report said.

Source: MENA