Ukrainian government forces have reclaimed the strategic port city of Mariopol from pro-Russian separatists.
Kyiv has also retaken control of a long stretch of the border with Russia after heavy fighting.
The gains are seen by many as a step closer to crushing the separatist rebellion and holding the country together.
Ukraine wants to regain full control of the 2,000 km border because it accuses Moscow of allowing rebels to bring tanks and guns across the border.
Parallel diplomatic talks are moving slowly, though, with Russia threatening to cut gas supplies to Ukraine from Monday in a row over prices.
Meanwhile, the Ukrainian Defence Ministry released a video which purports to show soldiers near the eastern city of Slavyansk engaged in a gun battle with separatists.
Ukrainian army and national guard soldiers in the video take cover behind armoured vehicles as they shoot over a valley towards separatists.