Seoul (AFP) – Russian President Vladimir Putin and North Korea's leader Kim Jong Un have vowed to strengthen cooperation, days ahead of Putin's summit in Alaska with Donald Trump, Pyongyang's state media reported Wednesday.

Putin and Kim spoke by phone in a "warm comradely atmosphere" on Tuesday and confirmed "their will to strengthen cooperation in the future", the official Korean Central News Agency (KCNA) said.

The call came three days before the summit between Putin and Trump, the first between a sitting US and Russian president since 2021, as Trump seeks to broker an end to Russia's more than three-year war in Ukraine.

North Korea has sent thousands of troops to Russia's Kursk region as well as weapons to aid its war effort, with Kim offering Moscow his full support for the war during talks last month with Russian Foreign Minister Sergei Lavrov.

During their call on Tuesday, Putin expressed appreciation for "the self-sacrificing spirit displayed by service personnel of the Korean People's Army in liberating Kursk", KCNA said.

Kim, in turn, pledged that North Korea would "fully support all measures to be taken by the Russian leadership in the future, too".

The Kremlin confirmed the phone call in a statement, adding that Putin had "shared information with Kim Jong Un in the context of the upcoming talks with US President Donald Trump".

The public disclosure of Kim and Putin's conversation signals the "intent to showcase their closeness to domestic and international audiences", Yang Moo-jin, president of the University of North Korean Studies in Seoul, told AFP.

Should Trump and Putin agree on a Ukraine peace deal, "Putin could convey Kim's stance on Trump's North Korea-related interests, potentially including a conditional summit on nuclear disarmament," said Yang.

Putin may also have been briefing Kim on matters of interest to the North Korean leader -- "mentoring him" in a way.

"If Russia-Ukraine peace talks gather momentum, they could have a positive spillover effect on US-North Korea and inter-Korean dialogue," he added.

During the US president's first term, Trump met Kim three times in a bid to reach an agreement on the denuclearisation of North Korea.

But since their second summit in Hanoi in 2019 fell apart over a failure to agree on what the North would get in return, Pyongyang has accelerated its nuclear programme.

Trump has talked up his "great relationship" with Kim, but the North Korean leader's powerful sister warned the United States late last month against pursuing denuclearisation, saying any push to deny the North its position as a nuclear weapons state would be "thoroughly rejected".

Kim Yo Jong said the "personal relationship" between her brother and Trump was "not bad", but warned that it should not be used to "serve the purpose of denuclearisation" in any future talks.

Relations between the two Koreas had been at one of their lowest points in years under former South Korean president Yoon Suk Yeol, with Seoul taking a hard line towards Pyongyang.

However, newly elected President Lee Jae Myung has taken a different approach, saying he would seek talks with the North without preconditions.