Ukrainian forces have reportedly destroyed a North Korean howitzer in a major blow to Putin's army.

       North Korea's President Kim Jong un has sent around 12,000 troops to Russia, as part of a security deal he signed with the Kremlin last year.

       Along with the troops, Pyongyang has also sent artillery shells, howitzers and ballistic missiles.

       Most of the North Korean troops have been deployed to the Kursk front, where they and their Russian counterparts are struggling to retake territory seized by Ukraine in a lightening incursion in August.

       However, some of the North Koreans may also be operating on the Kharkiv front in the Kupyansk area.

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       Ukraine's army says its troops have registered their first hit on a North Korean M1989 howitzer.

       The 170-millimetre artillery gun can fire shells weighing 100 pounds or more at least 25 miles.

       Drone operators from the 412th Unmanned Strike Aviation Battalion spotted the vehicle's heat signature while on night patrol.

       As the crew fled to safety, the drone dropped a bomb on the howitzer, which exploded into a ball of flames.

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       "We are accepting another 'Wunderwaffe' of the enemy military-industrial complex into the collection of Nemesis achievements," the drone battalion quipped, using the German term for "wonder weapon."

       North Korean weaponry is reportedly supporting Russia's 1st Guards Tank Army, as it tries to advance towards Kupyansk.

       The unit has been fighting to establish a bridgehead across the Oskil River in order to squeeze the Ukrainian garrison in the city.

       The Ukrainian Centre for Defence Strategies said on Monday that Russian forces had intensified their attacks on the front.

       It said: "They crossed the Oskil River and advanced in the fields southwest of Topoli, 20 miles north of the city."

       It comes amid reports that Russian troops failed to back up their North Korean counterparts during a fierce battle for a village in Kursk.

       North Korean soldiers were forced to retreat from their positions near a key village, after troops from Russia's 155th Brigade failed to show up and provide support.