Ukraine says the country’s intelligence services are in communication with fighters captured at the Azovstal plant in Mariupol and that Kyiv is doing all it can to ensure their release.

Uncertainty has surrounded the fate of hundreds of soldiers taken prisoner by Russian forces after they abandoned the steel-mill complex in the port city on the Sea of Azov last month.

“It is through [the intelligence services] that we are learning about the conditions of the detention, nutrition, and the possibility of their release,” Interior Minister Denys Monastyrskiy said on Ukrainian television late on June 3.

The minister said Ukrainian authorities were “doing everything possible” to secure their release.

Russia has said that some 2,500 Ukrainian soldiers have been taken into custody at the plant.

Ukrainian officials and relatives of the soldiers have urged Moscow to treat the men as prisoners of war. Kyiv wants them returned in a prisoner swap.

Some senior Russian lawmakers have demanded that some of the soldiers be put on trial. The Kremlin has said the fighters who surrendered will be treated according to international standards.

Russia said on May 20 that its forces had complete control of the massive factory following weeks of intense fighting in the city.

Ukraine has described the withdrawal from Azovstal as an authorized “evacuation,” rather than a surrender.