North Korea's Kim Jong Un plans to travel to Russia this month to meet President Vladimir Putin, a US official has told the BBC's US partner CBS.

The two leaders will discuss the possibility of North Korea providing Moscow with weapons to support its war in Ukraine, the official said.

The exact location of the planned meeting is not clear.

There was no immediate comment on the report, also carried by other US media, from North Korea or Russia.

Sources told the New York Times that Mr Kim was most likely to travel by armoured train.

The possible meeting comes after the White House said it had new information that arms negotiations between the two countries were "actively advancing".

National Security Council spokesman John Kirby said Russia's Defence Minister, Sergei Shoigu, had tried to "convince Pyongyang to sell artillery ammunition" to Russia during a recent visit to North Korea.

Weapons on display at the meeting included the Hwasong intercontinental ballistic missile, believed to be the country's first ICBM to use solid propellants. It was the first time Mr Kim had opened the country's doors to foreign guests since the Covid pandemic.

Mr Putin and Mr Kim have since exchanged letters "pledging to increase their bilateral co-operation", he said.

"We urge the DPRK to cease its arms negotiations with Russia and abide by the public commitments that Pyongyang has made to not provide or sell arms to Russia," Mr Kirby said, using an abbreviation for the North.

He warned the US would take action, including imposing sanctions, if North Korea did supply Russia with weapons.

There is concern both in Washington and in Seoul about what North Korea would get in return for such a deal, which may result in increased military cooperation between the two countries in Asia.

On Monday, South Korea's intelligence service briefed that Mr Shoigu had suggested Russia, China and North Korea hold joint naval drills, similar to those carried out by the US, South Korea and Japan.

Another fear is that Russia could supply North Korea with weapons in the future, at a time when Pyongyang most needs them.

More worrying still, Kim Jong Un may ask Mr Putin to provide him with advanced weapons technology or knowledge, to help him make breakthroughs in his nuclear weapons programme.

However, a deal could end up being more transactional than strategic. For now, Russia needs weapons, and sanctioned-starved North Korea needs money and food.

The New York Times reported that the meeting between Mr Kim and Mr Putin could take place in the port city of Vladivostok, on the east coast of Russia.

The newspaper's diplomatic correspondent, Edward Wong, told BBC News channel that an advance team of North Korean officials had travelled to Vladivostok and Moscow late last month.

They "included security officers who deal with the protocol surrounding travel of the leadership, so that was a strong sign for officials looking at this", Wong said.

Pyongyang and Moscow have both previously denied that the North is supplying Russia with arms for use in its war in Ukraine.