North Korea on Wednesday test-fired a submarine-launched missile 500 kilometers (around 300 miles) towards Japan, marking what weapons analysts described as a clear step forward for its nuclear strike ambitions.

North Korea on Wednesday test-fired a submarine-launched missile 500 kilometers (around 300 miles) towards Japan, marking what weapons analysts described as a clear step forward for its nuclear strike ambitions.

The flight distance, which was tracked by South Korea's military Joint Chiefs of Staff, far exceeded any previous SLBM tests, suggesting significant progress in technical prowess.

A proven SLBM system would take North Korea's nuclear strike threat to a new level, allowing deployment far beyond the Korean peninsula and a  "second-strike" capability to retaliate in the event of an attack on its military bases.

"While there are still a lot of questions about the details, this test certainly seems to have been successful," said Jeffrey Lewis, director of the East Asia Nonproliferation Program at the Middlebury Institute of International Studies in California.

"This system is still in development, but North Korea is clearly making progress," Lewis told AFP.

Current UN resolutions prohibit North Korea from any use of ballistic missile technology, but Pyongyang has continued to carry out numerous launches following its fourth nuclear test in January.

South Korea has responded by agreeing to deploy a sophisticated US anti-missile system -- known as THAAD -- a move that has seriously strained relations with North Korea's main diplomatic ally, China.

Lewis noted that an SLBM was an "effective countermeasure" to THAAD, and other missile systems with forward-looking radars, since the submarine can launch the missile from behind the radar.

Japanese Prime Minister Shinzo Abe said Wednesday's missile breached his country's Air Defense Identification Zone (ADIZ) and condemned what he called an "unforgivable, reckless act" and a grave threat to Japan's security.

Earlier this month, North Korea fired a land-launched ballistic missile directly into Japanese-controlled waters for the first time, drawing an outraged response from Tokyo.