The Russian Justice Ministry said the country’s Supreme Court would hold a hearing on May 26 on the question of outlawing the Azov Regiment, which spent weeks doggedly resisting Russia’s advance alongside other units at the steel plant and has drawn frequent contempt from Moscow.

Russian investigators said separately on Tuesday that they would interrogate all Azovstal fighters as they gather material toward criminal cases for “crimes against the civilian population of the Donbas,” a mostly Russian-speaking part of Ukraine that Moscow has repeatedly asserted, without evidence, is enduring a genocidal campaign by Kyiv.

While the Kremlin has promised to treat the Ukrainian fighters humanely, lawmakers and other officials have called on them to be placed on trial rather than be exchanged in the prisoner swaps that Ukraine has called for. How a terrorist designation will affect the punishment they face is unclear.