WASHINGTON (AP) — The White House on Wednesday said that it has new intelligence that shows Russian President Vladimir Putin and North Korean leader Kim Jong Un have swapped letters as Russia looks to North Korea for munitions for the Ukraine war.

National Security Council spokesman John Kirby detailed the latest finding just weeks after the White House said that it had determined that Russian Defense Minister Sergei Shoigu during a recent visit to Pyongyang called on North Korean officials to increase the sale of munitions to Moscow for its war in Ukraine.

Kirby said that Russia is looking for additional artillery shells and other basic materiel to shore up Russia's defense industrial base.

He added that the letters were "more at the surface level” but that Russian and North Korean talks on a weapons sale were advancing. The leaders exchanged the letters following Shoigu's visit, he said.

The Biden administration has repeatedly made the case that the Kremlin has become reliant on North Korea, as well as Iran, for the arms it needs to fight its war against Ukraine. North Korea and Iran are largely isolated on the international stage for their nuclear programs and human rights records.

In March, the White House said it had gathered intelligence that showed that Russia was looking to broker a food-for-arms deal with North Korea, in which Moscow would provide the North with needed food and other commodities in return for munitions from Pyongyang.

Late last year, the White House said it had determined that the Wagner Group, a private Russian military company, had taken delivery of an arms shipment from North Korea to help bolster its forces fighting in Ukraine on behalf of Russia.

Both North Korea and Russia have previously denied the U.S. allegations about weapons. North Korea, however, has sided with Russia over the war in Ukraine, insisting that the “hegemonic policy” of the U.S.-led West has forced Moscow to take military action to protect its security interests.