South Korean Navy soldiers and Marines take part in a landing exercise at Hat Yao Beach in Thailand on Feb. 11, 2016. A North Korean submarine went missing according to reports by U.S. officials that had been watching the vessel. It is unclear whether the submarine sank or is floating underwater, but officials believe it experienced some type of failure. The submarine's disappearance came after joint military drills between the U.S. and South Korea led North Korea to threaten "pre-emptive" strikes. Photo courtesy of the South Korean Marine Corps/Yonhap/UPI

WASHINGTON, March 12 (UPI) -- A North Korean submarine stationed off the nation's eastern coast was reported missing by United States military officials who observed the vessel.

U.S. officials told CNN North Korea lost contact with the submarine, as spy satellites, aircraft and ships watched North Korean navy searched the surrounding ocean.


It is believed the submarine experienced some type of failure, although it is unclear whether it sunk or is simply floating beneath the sea.

"The speculation is that it sank," a U.S. official said, according to Sky News. "The North Koreans have not made an attempt to indicate there is something wrong or that they require help or some type of assistance."

News of the missing submarine came after Pyongyang made statements regarding joint military drills between the U.S. and South Korea.

The drills, which involve 17,000 members of the U.S. military and 300,000 South Korean troops as well as 55 U.S. marine aircraft and 30 U.S. and South Korean ships, led North Korea to warn of "pre-emptive" strikes.

Since the drills have begun North Korea has fired two short-range ballistic missiles off the east coast of South Korea, as Kim Jong Un called for more nuclear tests.