Russian troops have taken more than 400 hostages in a major hospital in besieged Mariupol, regional leader Pavlo Kyrylenko said.
Locals were rounded up and brought to the the bomb-damaged hospital as troops opened fire, he said.
Mariupol, a key port city on the Black Sea coast, has been encircled by Russian forces for more than a fortnight and residents have had access to food, water and power cut off.
Meanwhile, Russia suggested it could allow a revival of the 2015 Iran nuclear deal in a shift from its previous demand that Western sanctions imposed over the invasion of Ukraine would block efforts to bring the deal back.
Foreign Minister Sergei Lavrov said Russia had written guarantees that it can carry out its work as a party to the deal.
Under the deal, Iran agreed to limit its nuclear program to make it harder to develop a nuclear bomb – an ambition it denies – in return for relief from global economic sanctions.
