Ukraine's Interior Minister Arsen Avakov said on Tuesday that at least 30 pro-Russian separatists have been killed in a renewed bout of fighting near Slavyansk.
"We estimate that the terrorists lost more than 30 people," Avakov wrote in a post on Facebook. Avakov said that four troops loyal to Kiev died in the fighting and that a further 20 were injured.
Ukrainian forces have been cracking down on rebel strongholds in the east of the country since early last week.
In a separate development, Russia said that it will move to bolster its Black Sea naval fleet with additional warships and submarines, according to the Interfax news agency, citing comments made by Russian Defense Minister Sergei Shoigu.
In Donetsk, a major city approximately 75 miles south of Slovyansk, flights from the local airport were suspended Tuesday.