At least 15 people have been killed and 46 injured in a series of rocket attacks by pro-Russian rebels in Ukraine’s government-held port of Mariupol, police there say.
The Grad rockets hit a market in a residential area in the east of the city, the police chief said.
A spokesman for the rebels denied that they had any involvement in the attack, calling it “blatant misinformation”.
More than 5,000 people have died in fighting in the east since April.
The rebels have seized a large swathe of the Donetsk and Luhansk regions. More than a million people have been displaced.
The main pro-Russian rebel leader in eastern Ukraine, Alexander Zakharchenko, said on Friday that his troops were on the offensive and that he did not want truce talks with Kiev.
A ceasefire agreed in Minsk in September but never fully took hold. Many hoped that the lower level of hostilities it introduced would last, but the BBC’s David Stern says that the fighting is beginning to approach what was seen last summer.
Mariupol has a population of 500,000 and is in a highly strategic position, sitting between rebel-held eastern areas and Crimea, which was annexed by Russia last March. The city saw heavy fighting in August.
Our correspondent says that if the hostilities move to Mariupol it will signal a major escalation in the fighting.
Unverified video footage on Saturday indicated that a number cars, houses and apartment buildings had been struck and were in flames.
Our correspondent says the attack appeared to come from a multiple-rocket launcher, which fires a large number of missiles over a spread-out area.
The rebels denied any involvement. Interfax news agency quoted the defence ministry of the Donetsk People’s Republic as saying: “This is blatant misinformation and a lie. Rebel forces did not open any fire in the direction of Mariupol, especially not on residential areas.”
One resident told Agence France-Presse by telephone: “Obviously, everyone in the city is very scared. The rebels have already seized the airport. And now they are starting to destroy Mariupol itself.”
The US ambassador to Ukraine, Geoffrey Pyatt, tweeted: “Today’s indiscriminate shelling of Mariupol part of an apparently Russian-backed general offensive in complete violation of Minsk agreements.”