A new threat made by North Korea is raising tensions in the region as U.S. President Barack Obama starts a major tour of Asia.

Obama said in an interview that North Korea's nuclear and missile programs pose a grave threat to Asian security. He’s called on Pyongyang to return to disarmament talks.

The two Koreas had their first naval fire fight in seven years on Tuesday along a disputed sea border off their west coast. A South Korean vessel was hit by bullets and a North Korean patrol ship caught fire.

The North's military said in a message carried by state-run TV, that it does not recognize a naval border set by the U.N. at the end of the Korean War.

"We will remind there is only one maritime military demarcation line in the West Sea as we have designated and we will from this point on be taking ruthless military actions to enforce it."

The sea border has been the site of two deadly naval battles between the Koreas in the past decade.