Artillery fire has killed at least four people in a residential area in eastern Ukraine, spurring more people to flee the besieged city of Donetsk and its suburbs.
Pro-Russian insurgents last week retreated from the strategic city of Slovyansk and holed up in Donetsk, a city of one million, and potentially the final frontier for the rebels. The overnight artillery strike in Maryinka, a western suburb of Donetsk, hit four apartment blocks near a rebel base. It was unclear which side fired at the buildings.
Journalists heard outgoing mortar fire from the area today, suggesting that the rebels sometimes fire at government troops from the residential area, prompting Ukrainian forces to return fire.
Fighting between the rebels and government troops has left more than 400 dead and tens of thousands have fled their homes, in many cases crossing the border into Russia.
The attack in Donetsk came hours after Ukraine's president, Petro Poroshenko, vowed vengeance for the deaths of 19 troops in an insurgent rocket attack near the Russian border.
"For every life of our soldiers, the militants will pay with tens and hundreds of their own," Mr Poroshenko said. "Not one terrorist will evade responsibility. Everybody will get what is coming to them."
Meanwhile, the European Union moved to impose sanctions on 11 leaders of the pro-Moscow rebellion.
Targets of the asset freeze and travel ban included two Russian spin doctors, Alexander Borodai, prime minister of the separatist Donetsk People's Republic, and his counterpart in the Luhansk People's Republic, Marat Bashirov.
Both formerly worked for Russian tycoons.
The names published in the EU's Official Journal brought the number of people subject to the bloc's Ukraine-related sanctions to 72, as well as two companies whose EU-based assets have been frozen.
A Russian diplomat criticised Brussels for the sanctions.
Vladimir Chizhov, the Russian envoy to the EU, said in comments carried by Interfax that Moscow believes in bringing peace to eastern Ukraine through negotiations, and that "blacklisting opponents isn't helping to build a dialogue with them".
Ukraine has refused to negotiate with rebels whom it describes as terrorists, although a Kiev envoy has taken part in a round table with Mr Borodai along with representatives of Russia and the Organisation for Security and Co-operation in Europe.
Rebels have rejected Ukraine's call to lay down their arms as a condition for ceasefire negotiations.