Heavy fighting has erupted in a suburb of the rebel stronghold of Donetsk, in eastern Ukraine, local officials say.
There are reports of civilian casualties as government forces battle to retake the city from pro-Russia separatists, the city council said.
Reports say powerful blasts and shooting were heard in the city.
Ukrainian government forces have made steady gains in recent weeks, encircling Donetsk and another rebel stronghold, Luhansk.
"As of 17:00 (14:00 GMT) in the Petrovksy district of Donetsk there are active military hostilities going on," Donetsk city council said on Tuesday, quoted by Ukraine's Unian news agency.
Electricity has been cut in some parts of the district after shells hit substations in the area, the agency adds.
It said that gunfire could also be heard in other parts of the city, including the use of heavy weapons.
At least 1,500 people, both civilians and combatants, are believed to have been killed and thousands more injured since Ukraine's new government sent in troops to put down the insurrection in the Donetsk and Luhansk regions in mid-April.
The rebels have since been pushed back to their strongholds in the two cities of the same name, though other pockets of resistance remain.
The region has been unstable since April, when rebels in the east declared independence from Kiev.