Ukrainian government forces have encircled the rebel-held port city of Mariupol.
Interior Minister Arsen Avakov, writing on Facebook, said Ukrainian troops had launched a dawn attack on the city on June 13.
Rebel forces confirmed fighting was under way, saying five separatists had been killed.
The rebels said they had blown up an armored personnel carrier carrying government soldiers and that "many" had been injured.
Meanwhile, Ukraine's military analyst Dmitry Tymchuk wrote on Facebook that Ukrainian security forces damaged two tanks that came earlier for fighters from Russia. The ATO forces also destroyed three armored personnel carriers; two trucks carrying militants and weapons; two vehicles mounted with heavy machine guns.