Krisztián L., 43, was convicted by a judge in Szekszárd for “prohibited recruitment into an armed group participating in armed clashes”.

Explaining the light sentence, the judge said that the crime is relatively unknown in Hungary and that the defendant was unaware that he had broken Hungarian law.

The prosecution lawyer appealed the verdict and is seeking a custodial sentence.

A native of Paks in central Hungary, the man was arrested last year at Budapest Ferenc Liszt International Airport on his return from fighting with the Donetsk People’s Republic secessionist group against the Ukrainian army.

A former policeman, he travelled to the breakaway province, whose de facto capital is Donetsk, in September 2015 where he received training and financial payments for his service.

The group is considered an illegal paramilitary group under Hungarian law, while the province has not been recognised as a sovereign state by Budapest.

The man was later wounded in action, recovered, and received military honours from the group.

More than 10,000 people have died since the insurgency in Ukraine began in April 2014.

Ukraine and its Western allies accuse Russia of funnelling troops and arms across the border to fan the flames of the conflict.

Moscow has denied the allegations despite overwhelming evidence that it has been involved in the fighting and its explicit political support for the rebels.