KIEV (AFP) - Fighting broke out on Friday in Ukraine's south-eastern port city of Mariupol, causing casualties, according to reports by Ukrainian and Russian media.
An online Ukrainian news website, Insider, said eight pro-Russian militants had been killed.
Russia's Interfax news agency said Ukrainian troops used large calibre weapons as they tried to take an occupied government building in the city.
Members of a crew from Britain's ITV News in the city said on Twitter that they saw heavy guns being used and smoke from burning tyres rising above Mariupol.
"Just filmed serious fighting downtown Mariupol. Snipers everywhere. Heavy guns. A man got shot just next to me. Black smoke over the city," wrote cameraman Daniel Demoustier.
Ukrainian military armoured vehicles were seen in the centre of Mariupol.
The fighting occurred as Ukraine commemorated Victory Day celebrations marking the Soviet defeat of German forces in World War II.
Kiev held low-key ceremonies while Russia - which the West accuses of fomenting Ukraine's insurgency - put on a diplay of military might in Moscow's Red Square.