Russian shelling set a central market ablaze in Ukraine's eastern city of Slovyansk, killing two people and injuring seven, an official said.
"This is pure terrorism!" Donetsk regional head Pavlo Kyrylenko said.
Mayor Vadym Lyakh said Slovyansk was being hit by Russian artillery salvoes from closer positions, as it became a frontline city.
He posted photos of Tuesday's blaze on Facebook, describing massive shelling, and urging people to stay in shelters.
Russia is seeking to capture all of the eastern industrial Donbas area.
The area is made up of two regions, Luhansk and Donetsk. After recognising two rebel self-proclaimed statelets there, Russian President Vladimir Putin ordered an invasion of Ukraine on 24 February.
Last week, Ukraine's military said it had to pull out of Lysychansk, its last remaining stronghold in Luhansk, under intense Russian fire.
It said its troops were now strengthening fortifications to defend areas it holds in Donetsk, including Slovyansk.
Luhansk regional head Serhiy Haidai on Tuesday said that "heavy fighting is going at the edge of the Luhansk region near Lysychansk".
"The enemy has deployed significant forces," he said, adding that Russia was trying to send more of its forces across a river by building pontoon bridges.
Mr Haidai said the Russians were "sustaining heavy losses".
The BBC has not been able to verify details of the latest attacks.
In other developments:
- In Russian-occupied southern Ukraine grain is being sent for export to the Middle East from the Zaporizhzhia region, Russian media report. Yevgeny Balitsky, a Moscow-appointed official, told Tass news agency that agreements had been reached with buyers in Iraq, Iran and Saudi Arabia. He said a deal with Iran involved supplying 150,000 tonnes of Ukrainian grain
- Turkish presidential adviser Ilnur Cevik told the BBC that Ankara may sell the grain carried in a Russian ship it detained over the weekend, and hand the proceeds to Kyiv, if proven to be Ukrainian. The Zhibek Zholy is carrying 7,000 tonnes of grain and had left Berdyansk, a Ukrainian port seized by Russia
- The foreign ministers of Finland and Sweden launched the process for their countries to join Nato at a ceremony in Brussels. But the parliaments of all 30 Nato members first have to ratify their accession, and Turkey is demanding the handover of more than 70 opposition exiles living in the Nordic countries. They are on a Turkish list of suspects with alleged "terrorist" links
- The Russian parliament's lower house, the Duma, has backed a draft law allowing for "special measures" in industry to support the Russian military in Ukraine. The state would be able to enforce longer working hours and impose contracts on certain enterprises linked to what Russia calls its "special military operation" in Ukraine.