North Korea threatened on Tuesday to engulf the southern islands on the border with Pyongyang in a “sea of flames” in case a “single shell” falls on the communist state’s side, during a joint drill between Seoul and Washington.

North Korea threatened on Tuesday to engulf the southern islands on the border with Pyongyang in a “sea of flames” in case a “single shell” falls on the communist state’s side, during a joint drill between Seoul and Washington.

“Any subsequent counterstrike would trigger an escalated military reaction that would see South Korea's border islands engulfed in a "sea of flames," said a statement from the southwestern command of the Korean People's Army.

South Korean live-artillery exercises near the Yellow Sea border were an attempt to tip prevailing military tensions into an "actual war," said the statement carried by the official Korean Central News Agency.

North Korean troops in the sector have been ordered to take "immediate counteractions in case even a single shells drops" across the border, it said.

"In case the enemies recklessly counter our counterstrikes, all striking forces will turn the (South's) five islands ... into a sea of flames," the army statement said.

The five islands lie near the disputed border that was the scene of bloody naval battles in 1999, 2002 and 2009.

South Korea and the United States are reportedly staging a five-day joint anti-submarine drill until Friday near the maritime border, involving a US nuclear-powered attack submarine, the USS Bremerton, and a number of warships.