Civilians flee eastern Ukraine ahead of new Russian offensive

Russian troops also continued to pound the Azovstal industrial district of Mariupol where Ukrainian marines were making a last stand in the defence of the strategic port, largely reduced to rubble after six weeks of bombardment.

Russia is believed to be trying to seize Mariupol to connect occupied Crimea with the self-proclaimed republics in Donetsk and Luhansk in the eastern Donbas region. Kyiv, however, said its defence of the stricken city was continuing.

Mariupol city hall said the area where the poisonous substance had allegedly been used could not be examined because of enemy fire. Ukrainian soldiers who had come into contact with it were being observed for possible symptoms, it said.