At least 15 people were killed when Russian rockets destroyed an apartment building in an eastern Ukrainian town.
The governor of the Donetsk region, Pavlo Kyrylenko, said more than 20 people could be trapped in the rubble of the five-storey building in the town of Chasiv Yar.
The rocket assault on Saturday night marks the latest in a recent burst of high-casualty attacks on civilian structures.
Images from the scene show rescue services searching through rubble using tractors and other machinery.
Mr Kyrylenko said the town of about 12,000 people was hit by Uragan rockets, which are mounted on and fired from trucks.
The town of Chasiv Yar is around 20km southeast of Kramatorsk, a city that is expected to be a major target of Russian forces as they grind westward.
Russia has repeatedly claimed it is only hitting targets of military value in the war.
Attacks on civilian areas
In late June, at least 19 people died when a Russian missile hit a shopping centre in the city of Kremenchuk and 21 people were killed when an apartment building and recreation area came under rocket fire in the southern Odesa region this month.
The Donetsk region is one of two provinces along with Luhansk that make up the Donbas region, where separatist rebels have fought Ukrainian forces since 2014.
Last week, Russia captured the city of Lysychansk, the last major stronghold of Ukrainian resistance in Luhansk.
After the seizure of Lysychansk, some analysts predicted Moscow's troops would take some time to rearm and regroup.
Russia's mission to take Donbas continues
While Russia and Ukraine blame each other for the killing of civilians in the Donbas region, Moscow has voted to continue its fight in the region.
Russia's ambassador to the UK said his country is unlikely to withdraw from Ukraine's southern coast.
Andrei Kelin said: "We are going to liberate all of the Donbas.
"Of course it is difficult to predict the withdrawal of our forces from the southern part of Ukraine because we have already experienced that after withdrawal, provocations start and all the people are being shot and all that."