A U.N.-backed human rights expert decried violence in Russia by former convicts whose sentences are commuted to fight in Ukraine who then return home to commit crimes including rape and murder.

Ukraine accused Russia at an international court on Monday of flouting sea law by trying to keep the Kerch Strait between mainland Russia and annexed Crimea under its sole control. Kyiv began proceedings at the Hague-based intergovernmental Permanent Court of Arbitration in 2016 after Moscow began building the 19 km (12 mile) Crimea Bridge link to the peninsula it seized from Ukraine two years previously.