Austrian prosecutors confirmed Sunday's arrest at Dorohusk, a crossing on Poland's eastern border with Ukraine, but the context of the suspect's alleged crimes remained unclear.

The man is alleged to have killed captured and wounded soldiers near the airport in Donetsk, the scene of clashes between pro-Russian rebels and Ukrainian forces dating back to 2014.

The Polish news agency PAP first reported the arrest. The French news agency AFP initially said the man had fought with rebels, but Reuters later reported the man had fought on the Ukrainian government's side.

He was accused of "having killed soldiers involved in fighting at the Donetsk airport who had already surrendered and/or of having killed civilians," a spokesman for the Prosecutors Office in the province of Lower Austria said.

Low-intensity fighting

Moscow has been propping up pro-Russian rebels in the Donetsk and Luhansk region since the conflict began in April 2014, although the Kremlin has denied sending troops or weapons to the fighters.

The war began after Russia annexed Ukraine's Crimean Peninsula in 2014, securing its large military naval base.

Close to 10,000 people have been killed in the conflict. 

The insurgent territories are home to nearly 4 million people and account for about a tenth of Ukraine's total population.

The conflict has settled into low-intensity fighting that European leaders who helped draft a February 2015 peace agreement have been unable to stop.

ipj/sms (Reuters, AFP, dpa)