Seoul, South Korea - North Korean leader Kim Jong Un oversaw tests this week of his country's naval destroyer, claiming Pyongyang is in the process of "arming the Navy with nuclear weapons", state media reported Thursday.

The tests, including a launch of a sea-to-surface cruise missile, come shortly after Kim led a major once-in-five-years Party Congress, at which he renewed goals of a military buildup and vowed to forcefully respond to any threats.

It also comes as the nuclear-armed North's key foe – the US – launched its joint offensive with Israel against Iran, aiming to wipe out the Islamic republic's nuclear program, missiles, and navy.

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Kim inspected on Tuesday a "Choe Hyon" class ship – one of two launched last year – and oversaw a "shakedown" or performance test, the Korean Central News Agency reported.

"The arming of the Navy with nuclear weapons is making satisfactory progress," Kim said, according to KCNA.

"All these successes constitute a radical change in defending our maritime sovereignty, something that we have not achieved for half a century," he added.

The following day, he oversaw the missile launch from the ship, which was "successfully carried out," KCNA said.

The Choe Hyon is one of two 5,000-ton destroyers in the North's arsenal, both launched last year as Kim seeks to ramp up the country's naval capabilities.

A third vessel is under construction, which Kim also visited on Wednesday, according to KCNA.

Pyongyang has previously said the Choe Hyon is equipped with the "most powerful weapons".

Some analysts said the ship could be equipped with short-range tactical missiles capable of carrying nuclear warheads – although North Korea has not proven it has the ability to miniaturise its atomic arsenal.

Pyongyang last week condemned the ongoing US and Israeli attack on Iran as an "illegal act of aggression", claiming it had shown Washington's "rogue" nature.

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Kim's latest move involving the ship appears to be "intended as a show of force amid the ongoing Iran situation and ahead of upcoming South Korea-US joint military drills," Yang Moo-jin, former president of the University of North Korean Studies, told AFP.

Pyongyang and Washington are longtime adversaries but the US has mounted a push to revive high-level talks with the North in recent months.

Reports and analysts have suggested the US is eyeing a potential summit between US President Donald Trump and the North's Kim this year.

After largely ignoring those overtures for months, Kim said last month that the two nations could "get along" if Washington accepted Pyongyang's nuclear status.