A Polish soldier who was stabbed on the country’s border with Belarus in May has died from his injuries, Poland’s military announced on Thursday.

It said the soldier was allegedly stabbed in the chest by a migrant who reached through a fence erected on the border to prevent illegal crossings.

The Polish Foreign Ministry said it had summoned the Belarusian charge de’affaires, demanding Minsk authorities hand over the soldier’s killer.

Poland and the EU claim many of the migrants attempting to cross into the country are organized and aided by Russia and its ally Belarus as part of an attempt destabilize Europe.