More than 20 Ukrainian soldiers have been killed during clashes with pro-Russia activists in the troubled eastern regions, despite an ongoing ceasefire between the two sides.
The fighting took place near a government checkpoint around the flashpoint city of Slavyansk.
Reports say two Ukrainian armored vehicles were also destroyed during the clashes.
Armed men said Ukrainian troops were forced out of the area, but Kiev officials say government troops repelled the attack.
The renewed fighting comes despite an ongoing truce between Kiev and pro-Russia activists in the country’s troubled southeastern regions.
Ukraine’s mainly Russian-speaking parts in the east have been the scene of deadly clashes between pro-Russia activists and the Ukrainian army since Kiev launched military operations in mid-April in a bid to crush the pro-Russia protests.
The violence intensified after the Donetsk and Lugansk regions held local referendums on May 11, in which their residents voted overwhelmingly in favor of independence from Ukraine. The referendums echoed a March vote in Crimea that led to the reunification of the peninsula with the Russian Federation.
The government in Kiev says it is targeting armed protesters, but reports say many civilians have been caught in the shelling that has been going on for days.
According to figures released by the United Nations, an estimated 423 people have been killed between April 15 and June 20 in eastern Ukraine.
In addition, the Office of the United Nations High Commissioner for Refugees says some 110,000 Ukrainians have so far fled to Russia this year.