Ukraine's defense intelligence agency has released an audio clip of what it claims to be intercepted radio communications between North Korean soldiers in Russia speaking in coded military terms.

The Defense Intelligence of Ukraine uploaded a post on Sunday (local time) of what it claimed to be intercepted radio transmissions of a group of North Korean soldiers deployed in Russia's western Kursk region to support Russia's war against Ukraine.

In the audio, the soldiers exchange coded terms in the North Korean accent, such as "Mulgae hana, Mulgae dul," which translate to "Seal one, Seal two" in English, presumably to check their signals. One of the soldiers says, "Wait," apparently giving instructions to his subordinate.

The DIU said it intercepted the radio communications of the North Korean soldiers the previous day and claimed that the signals were about "ordering them to return immediately."

Ukraine and the United States believe some 11,000 North Korean troops have been sent to support Russia's war against Ukraine and they are deployed in the Kursk border region, where Moscow has been struggling to take back the part of the territory from the Ukrainian forces.

Ukraine has occupied parts of the Kursk region since launching its offensive in August.

The Ukrainian military has claimed the deployed North Korean troops are likely to engage in battle in the coming days.

The Pentagon has confirmed that a "small number" of North Korean troops are in the front lines and suggested they might be used in "some type of infantry role."

On Sunday, The New York Times reported that the Russian military has assembled some 50,000 soldiers, including North Korean troops, to launch an assault to reclaim the Kursk territory seized by Ukraine, citing US and Ukrainian officials.

CNN also carried a similar report, citing an unidentified US official, that Russia has gathered a "large force of tens of thousands" of its troops and North Korean soldiers to take part in an assault soon. (Yonhap)