Pyongyang, North Korea - North Korean ruler Kim Jong-un has accused the US of making the waters surrounding the peninsula "unstable" with its joint military exercises with South Korea, increasing the risk of a nuclear war.

In a speech to mark North Korea's Navy Day, Kim said that "the reckless confrontational moves" of the US and "other hostile forces" turned the waters around the Korean Peninsula "into the world's biggest war hardware concentration spot, the most unstable waters with the danger of a nuclear war," as reported by state-controlled media on Tuesday.

Kim also decried a recent announcement by "the gang bosses" of the US, Japan and South Korea of regular joint military exercises.

The North Korean ruler said the situation requires his country's naval force to be strengthened and prepared "to break the enemy's will for war in contingency."

At a tripartite summit earlier in August at Camp David near Washington DC, US President Joe Biden, Japanese Prime Minister Fumio Kishida, and South Korean President Yoon Suk Yeol agreed to significantly strengthen their security cooperation.

Last week, North Korea tested a strategic cruise missiles as part of a drill which observers saw as a response to an 11-day joint military exercise by South Korea and the US.

North Korea regularly accuses the two countries of using their exercises to prepare for an attack, something Seoul and Washington deny.

UN resolutions prohibit North Korea from testing ballistic missiles of any range, some of which are capable of carrying a nuclear warhead.

Tests of cruise missiles are not subject to sanctions against Pyongyang. Such weapons, however, can also be used to deliver nuclear warheads.