A Russian soldier who claims to have avoided detection in Ukraine's Kharkiv region for six months has been detained, Ukrainian police say.

The 42-year-old serviceman was stopped by members of the Ukrainian armed forces while they were patrolling the Kupiansk district, Kharkiv's regional police department said.

The area was retaken by Ukrainian forces last September.

The soldier told police he had hidden in abandoned buildings since then.

After they found him on Monday, police discovered that the man - dressed in civilian clothes - was a serviceman with Russia's 27th Separate Guards Motor Rifle Brigade and was a resident of the Moscow region.

The soldier was taken to a local police station for further investigation, a police statement said.

Kupiansk - home to an important railway junction - has witnessed fierce fighting since the war began last year, with Russia taking control in a matter of days, and occupying the town for several months.

Though the area was retaken by Ukrainian troops last September, it is under threat from Russian attempts to retake it once more.

Some residents were ordered to leave the area due to the "unstable security situation" by Ukrainian officials earlier in March.

On Tuesday, the head of Kharkiv's regional administration, Oleg Sinegubov, said the city - along with others in the region - was under fire from Russian troops.