ZAGREB, Croatia (AP) — A Croatian citizen who fought alongside Ukrainian troops in Mariupol has been detained by the Russian army, Croatian state media reported Saturday.

Croatia’s Foreign Ministry also confirmed that it “has knowledge of a detained Croatian citizen,” and is working with the Ukrainian authorities to resolve the situation. It offered no further information due to “sensitivity of the situation.”

The state HRT television reported that the Croatian man tried to flee Mariupol with other Ukrainian fighters but was caught by the Russians. No other details were immediately available.

The N1 regional television said the arrest was first reported by Russian media.

The strategic port of Mariupol has faced weeks of Russian bombardment. The attacks have intensified on embattled resisting troops in a steel factory in the city as Russian troops seek to fully conquer Mariupol in time for Russia’s Victory Day celebrations on Monday celebrating the 1945 defeat of Nazi Germany.