WASHINGTON (AP) — The White House said on Friday that North Korea has delivered more than 1,000 containers of military equipment and munitions to Russia for its ongoing war in Ukraine.

Speculation about a possible North Korean plan to refill Russia’s munition stores drained in its protracted war with Ukraine flared last month, when North Korean leader Kim Jong Un traveled to Russia to meet President Vladimir Putin and visit key military sites.

White House National Security Council spokesman John Kirby said that the U.S. believes Kim is seeking sophisticated Russian weapons technologies in return for the munitions to boost North Korea’s nuclear program.

The White House released images that it said show the containers were loaded onto a Russian-flagged ship before being moved via train to southwestern Russia. The containers were shipped between Sept. 7 and Oct. 1 between Najin, North Korea, and Dunay, Russia, according to the White House.

The U.S. has accused North Korea of previously providing ammunition, artillery shells and rockets to Russia.

Kim last month, after he had met with Putin, called for an exponential increase in production of nuclear weapons and for his country to play a larger role in a coalition of nations confronting the United States in a “new Cold War,” North Korean state media said.

The Korean Central News Agency said Kim made the comments during a two-day session of the country’s rubber-stamp parliament, which amended the constitution to include his policy of expanding the country’s nuclear weapons program.

In Russia, Kim deepened “comradely fellowship and friendly ties” with Putin, North Korean state media reported.

During Kim’s six-day trip to Russia, his longest foreign travel as a leader, the two countries said they discussed boosting their defense ties but didn’t disclose any specific steps. Foreign experts speculate the two countries, both locked in confrontations with the West, were pushing to reach arms transfer deals in violation of U.N. Security Council resolutions.