North Korea fired multiple cruise missiles into the sea on Wednesday, Seoul's military said in a statement, marking the latest in a string of weapons tests conducted under leader Kim Jong Un this year.

"Our military detected several unknown cruise missiles over the waters northeast of Wonsan around 09:00 today (0000 GMT/UTC) and South Korea-US intelligence authorities are conducting a detailed analysis," South Korea's Joint Chiefs of Staff said in a statement.

It further said that South Korea's military was "strengthening surveillance and vigilance, and closely watching for any additional signs and activities from North Korea." This was its fifth test of such weapons since January, the military said.

It wasn't immediately clear either whether the missiles were fired from land or from sea assets.

North Korea is subject to international sanctions because of its nuclear weapons and missile program. However, unlike ballistic missiles, cruise missiles tests are not directly affected by the UN restrictions. 

North Korea's growing aggression

Pyongyang has also been upping its rhetoric, with leader Kim Jong Un calling South Korea "our principal enemy" early in January, and threatening to annihilate its southern neighbor if provoked.

North Korea has also ramped up weapons tests which include cruise missiles, what it claims to be an "underwater nuclear weapon" delivery system and a solid-fuelled hypersonic ballistic missile.

The cruise missile launches have also prompted speculation non whether Pyongyan could be testing weapons before shipping them to Moscow for use in Ukraine.

At a time when Kim Jong Un has shown rising aggression towards the South and US, his relationship with Russia has simultaneously strengthened. Kim made a rare trip to Moscow to meet President Vladimir Putin in September.

Seoul and Washington have previously accused North Korea of supplying Russia with weapons in exchange for support for Kim's satellite programme — which would violate several UN sanctions against both regimes. 

mk/msh (AFP, AP, dpa)