Acting President Oleksandr Turchynov said on May 15 that security forces overnight destroyed a rebel base near Slovyansk.
He said the soldiers were also now controlling a 5-kilometer zone around a television tower south of the city that had been seized by the separatists.
He said the tower was now transmitting Ukrainian channels. The separatists had changed the signals to broadcast only Russian state TV.
The Defense Ministry said its forces also destroyed a rebel hideout outside the nearby city of Kramatorsk and had captured three "terrorists." The ministry said there were no casualties among the soldiers.
The fresh fighting came one day after the government launched a "national dialogue" to de-escalate the crisis.
The separatists, however, were not represented at the talks.
Turchynov said the government was ready for dialogue but would not bow to "blackmail" by pro-Russian rebels.
The government says it will not talk to the separatists until they lay down their arms. The separatists say the government must first withdraw its troops.
The roundtable talks are based on an Organization for Security and Cooperation in Europe (OSCE) road map to de-escalate the crisis ahead of Ukraine's May 25 presidential election.
Swiss Foreign Minister Didier Burkhalter, who is the OSCE's chairman in office, said the roundtable meeting in Kyiv on May 14 "allowed for constructive and engaged discussions and set the tone for the following editions to take place in the regions."
Burkhalter expressed hope that an "inclusive national dialogue" would help stabilize the political situation ahead of a presidential election set for May 25.
WATCH: After pro-Russian separatists in Donetsk asked Moscow to allow their self-declared "republic" to join the Russian Federation, RFE/RL's Ukrainian Service asked Donetsk residents if they thought their region should stay in Ukraine or join Russia. Meanwhile, a self-styled separatist commander in Donetsk, Sergei Zdrilyuk, has issued a 24-hour ultimatum for all government troops to withdraw and dismantle their checkpoints.
If they do not, he said, "all of this will be destroyed and burnt down."
NATO Secretary-General Anders Fogh Rasmussen, speaking on May 15 at a security conference in Bratislava, criticized Russia for not taking steps to de-escalate the crisis.
He also called on Central European states to increase their defense spending as Russia increases its own military budget.