Moscow, Russia - Russia on Friday refused to say whether North Korean troops were fighting alongside its army against Ukraine, a day after Kyiv claimed inflicting "losses" on Pyongyang's soldiers.

The West, Ukraine, and South Korea – citing intelligence reports – have said that North Korea has sent more than 10,000 troops to Russia to be deployed for combat.

Ukrainian President Volodymyr Zelensky said Thursday that some had already engaged in fighting in Russia's western Kursk region, where Kyiv has launched an offensive.

"North Korean army soldiers are currently present on the territory of the Russian Federation ... namely in the Kursk region," Zelensky told reporters.

Russia Putin meets with North Korea in Moscow as Ukraine troops tensions heat up

There are "11,000 of them. Some of these troops have already taken part in hostilities against the Ukrainian military. Yes, there are already losses," he added.

Asked by AFP about Zelensky's comments on Friday, Kremlin spokesman Dmitry Peskov declined to comment.

"This question directly concerns the course of the special military operation, therefore it needs to be addressed to the defence ministry," Peskov said, using Moscow's preferred language for its offensive.

Russia's defence ministry typically never responds to press enquiries regarding the conduct of the offensive.

Russian President Vladimir Putin and other senior Russian officials have repeatedly refused to outright deny reports of any North Korean troops fighting against Kyiv's army.

Zelensky has pressed Kyiv's Western backers to up their support in the face of North Korea's engagement, casting it as a major escalation that threatens global security.

Russian lawmakers earlier this week voted to ratify a landmark defense pact with North Korea that obliges both countries to provide immediate military assistance if the other is attacked.