Ukraine has resumed a military offensive against pro-Russian forces in the country's east on Saturday.
The move comes as military observers from the Organization for Security and Cooperation in Europe who were held for more than a week were released.
According to Fox News, Interior Minister Arsen Avakov said Ukrainian forces had seized control of a television tower in Kramatorsk, near the rebel stronghold of Slovyansk.
On his Facebook page, Avakov said that they were not stopping.
News reports claimed additional fighting broke out in the city of Kramatorsk, south of Slovyansk, on Saturday.
According to the report, tensions were especially high after at least 42 people died in clashes between government supporters and opponents in the Black Sea port of Odessa on Friday.
The city's police chief, Petr Lutsyuk, issued a statement calling for calm in the city, but hours later he was fired by Avakov.
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Meanwhile, insurgent leader Vyacheslav Ponomarev announced that all seven military observers and their five Ukrainian assistants had been released, the report said.
The observers were seized on April 25 in the city of Slovyansk, the epicenter of eastern Ukraine's unrest, as they traveled with an Organization for Security and Cooperation in Europe observer team.
At Russia's request, the U.N. Security Council met in an emergency session Friday on Ukraine.
Russian ambassador Vitaly Churkin demanded a "swift halt of all violence," but Western powers scoffed at his country's indignation, the report added.