North Korean leader, Kim Jong Un, is set to visit Vladimir Putin in Russia to discuss supplying weaponry for the Ukraine war, officials say.

Mr Kim would travel from Pyongyang North Korea’s capital by armored train to Vladivostok on the east coast of Russia where he would meet with Mr Putin, the New York Times reports. 

Mr Putin wants Mr Kim to agree to send Russia artillery shells and antitank missiles, and the latter would like Russia to provide North Korea with advanced technology for satellites and nuclear-powered submarines.

According to officials, Mr Kim is also seeking food aid for his impoverished nation.

Both leaders would be on the campus of Far Eastern Federal University in Vladivostok to attend the Eastern Economic Forum, which is scheduled to run from September 10 to 13.

This came after the White House warned that Messrs Putin and Kim had exchanged letters discussing a possible arms deal, citing declassified intelligence.

John F. Kirby, a spokesperson for the White House, who cited declassified intelligence, said high-level talks on military cooperation between the two nations were “actively advancing.”

Although, the U.S. official declined to give details on the state of personal ties between the leaders, who are considered adversaries of the United States.

It also declined to provide details on how spy agencies had collected the information.

But the latest development about their planned meeting goes far beyond the previous warning by the U.S. government.

While the White House declined to discuss the new intelligence, Adrienne Watson, a National Security Council spokeswoman, acknowledged that the United States expected “leader-level diplomatic engagement” on the issue of arms sales to take place between Russia and North Korea.

“We urge North Korea 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,” Ms Watson said in a statement.

U.S. officials say White House warnings about planned transfers of North Korean artillery shells stopped previous cooperation between Pyongyang and Moscow.

At other times since Russia began its full-scale invasion of Ukraine, the U.S.

Meanwhile, officials have released declassified intelligence to try to dissuade North Korea, China and other countries from supplying Russia with weapons.

In late August, a delegation of about 20 North Korean officials, including some who oversee security protocols for the leadership, travelled by train from Pyongyang to Vladivostok, and then flew to Moscow, an indication that North Korea was serious about a visit by Mr Kim.

Their trip, believed to be a planning expedition, took about 10 days, according to officials briefed on the intelligence reports.

Officials said the idea for the Russia visit came out of a trip by Sergei K. Shoigu, the Russian defence minister, to North Korea in July for Mr Kim’s celebration of the 70th anniversary of the “victory” over South Korean and U.S. forces in the Korean War.

Mr Putin has characterised his war against Ukraine as one of protecting Russian sovereignty since in his view Ukraine should be part of a restored Russian Empire.

In June, Mr Kim sent Mr Putin a message on Russia’s national day in which he pledged to “hold hands” with the Russian leader and promised that the Russian people would have North Korea’s “full support and solidarity” for their “all-out struggle.”