North Korea warned it could stage an “unimaginable strike” against the United States at an unexpected time, ratcheting up its warlike rhetoric as South Korea and the US stage a joint naval exercise in waters off the Korean Peninsula.

According to the state-run Korean Central News Agency on Thursday, North Korea’s “emergency committee for opposing war drills” denounced the allies’ ongoing military exercise and US dispatch of strategic assets as an attempt to provoke another war on the peninsula.

“The US is running amok by introducing under our nose the targets we have set as primary ones. The US should expect that it would face (an) unimaginable strike at an unimaginable time,” the agency said in a statement carried by the KCNA.

North Korea has long accused the joint drill of being a dress rehearsal for invasion despite the allies’ reiteration that it is defensive in nature. Last week, Pyongyang renewed its threat to fire a missile toward the US territory of Guam, saying the exercise would compel them to “take military counteraction.”

South Korea and the US military have since Monday kicked off a five-day joint naval exercise in waters east and west of the peninsula. The exercise involves the nuclear-powered aircraft carrier USS Ronald Reagan and its carrier strike group.

In response to the drill, North Korea has begun distribution of live ammunition to its military and secret police, Japanese newspaper Asahi Shinmun reported Thursday, citing an anonymous source with knowledge of North Korea.

“It is like a measure taken during the semi-war situation,” said the source, explaining that live ammunition is usually reserved for those serving at front-line units and military posts stationed along the borders between the two Koreas and its neighbors.

The communist country has also been suspected of constructing a new diesel-electric submarine at Sinpo shipyard on the country’s east coast, the Diplomat reported Wednesday, citing a US government source with knowledge of the North’s weapons programs.

According to current US intelligence estimates, the magazine reported, the submarine’s submerged displacement is thought to be in excess of 2,000 tons with a beam measurement of 11 meters. The vessel is likely the largest to be built for the Korean People’s Navy since the Najin-class frigates.

Since its sixth nuclear test and following ballistic missile launch in September, North Korea has not staged a major provocation, despite speculation it might do so during the Chinese twice-a-decade party gathering that kicked off Wednesday.

By Yeo Jun-suk (jasonyeo@heraldcorp.com