The UK defense ministry says that North Korea is emerging as one of the major suppliers of weapons supporting Russia's invasion of Ukraine.

The warning came on Thursday amid allegations that Russia has received military aid from North Korea to resupply its dwindling weapons stockpiles. Russia is now believed to be ramping up its attacks in the eastern region of Donetsk and other parts of Ukraine.

The ministry said North Korea "will be on course to become one of Russia's most significant foreign arms suppliers, alongside Iran and Belarus" if it "sustains the recent scale and pace of military-related shipments."

The ministry said "it is almost certain that North Korean munitions have now reached ammunition depots in western Russia." It added that the "depots support Russian military operations in Ukraine."

The top diplomats of Japan, the United States and South Korea strongly condemned North Korea's provision of military supplies to Russia.

The officials said in a statement that they have confirmed the completion of several such deliveries. They said the provisions "will significantly increase the human toll of Russia's war of aggression."

The foreign minister of Lithuania, one of the three Baltic states bordering Russia, called for quicker supplies of military aid to Ukraine.

Gabrielius Landsbergis wrote on social media that the European Union had promised 1 million artillery rounds to Ukraine, but only 300,000 have been delivered. He added that North Korea provided 350,000 rounds to Russia.

White House National Security Council spokesperson John Kirby told reporters on October 13 that North Korea had transported more than 1,000 containers of military supplies to Russia.

On Thursday, Kremlin spokesperson Dmitry Peskov declined to comment on the latest accusation, saying there are many reports about North Korea's military provisions to Russia which are ''all groundless." But he said that Russia and North Korea will continue to develop close relations in all areas.