At least 30 killed and more than 90 wounded in rocket attack on Mariupol

Grad rockets rained down on residential areas of the Ukrainian city of Mariupol on Saturday, killing at least 30 and wounding more than 90, according to local authorities.

The rockets, apparently fired by pro-Russia rebels, came on the day their leader announced an assault on the city, despite earlier denials from rebel authorities that they were responsible.

“Today an offensive was launched on Mariupol. This will be the best possible monument to all our dead,” said Alexander Zakharchenko, speaking at a memorial event for those killed in a mortar attack on a trolleybus stop in the rebels’ capital Donetsk on Thursday.

At least eight people died in that attack, which rebels say was carried out by a Ukrainian “diversionary group” operating inside the city. Kiev said the rebels carried out the attacks themselves, with the prime minister Arseniy Yatsenyuk calling it an act of “Russian terrorism”.

Ole Solvang of Human Rights Watch, who visited the scene of one of the rocket attacks in Mariupol, said he counted at least 20 craters spanning several blocks, with a market and a school among the places hit. The craters clearly showed the rockets had been launched from an easterly direction, Solvang said, further suggesting that they were fired from inside separatist-controlled territory.

Later in the evening, Zakharchenko made another U-turn, saying there would be “no storm” of Mariupol. Rebels and Russian television claimed the Ukrainians had shelled their own territory by mistake. However, the OSCE monitors, who visited the scene, were clear that the missiles had been launched from rebel territory.

Both sides have used Grad missiles during the conflict, which fire a salvo of up to 40 rockets across a wide area and are notoriously imprecise. According to the UN, more than 5,000 people have died, more than 10,000 have been injured and about a million displaced from their homes since the violence in east Ukraine began last spring. A ceasefire agreed in Minsk last September has never fully held, and over the past fortnight the situation has threatened to return to full-scale war.

Mariupol saw clashes last spring, but has remained under Ukrainian government control. Late in the summer, a rebel advance with apparent Russian backing moved down the coast to the outskirts of the city, but Kiev has said it will defend the city.

Privately, rebel sources told the Guardian in recent weeks they would not attempt to take the city as it would require the sort of urban warfare that would leave it destroyed and hundreds dead.

However, seizing Mariupol would give the Donetsk rebels access to the sea and pave the way for a potential land route between Russia and annexed Crimea.

With close links to Moscow and supplies of military hardware coming from Russia, it is unlikely the rebels would have begun such a major offensive without Russia’s backing. Ukraine’s president, Petro Poroshenko, has also claimed there are 9,000 regular Russian soldiers operating in east Ukraine, though Moscow has repeatedly denied there are any.

“The world needs to stop the Russian aggressor threatening Ukraine, Europe and global security … The problem is in the hero-town of Moscow-Kremlin, Vladimir Putin,” said Yatsenyuk at a meeting of security and defence chiefs on Saturday, in response to the attack on Mariupol.

Putin, speaking on Friday, insisted that the blame for the surge in violence lay with Ukraine.

“The Kiev authorities have given an official order to start large-scale military operations practically throughout the whole line of contact,” said Putin in televised remarks. However, it is the rebels who have seemed to be on the offensive in recent weeks, beginning with a surge to take back control of Donetsk airport, held by Ukrainian forces since the start of the conflict.

On Friday, Zakharchenko said the rebels would attack to prevent a Ukrainian attack in March or April, when new conscripts to the army have been called up. Zakharchenko said there will be “no more talk of ceasefire” and the rebels would advance to the “borders of Donetsk region”, an area that includes Mariupol and a number of major towns to the north of Donetsk currently under Kiev’s control.

Unwilling to enter military confrontation with Russia, the west has struggled to find ways to respond to Putin’s moves in Crimea and east Ukraine. Economic sanctions have combined with falling oil prices to deal a serious blow to the Russian economy in recent months, leading many to suspect that Putin might be looking for a way out of the east Ukraine quagmire. However, the events of the past week suggest the Russian leader is doubling down.

The shelling of Mariupol drew concerned responses from western capitals. The increased violence “would inevitably lead to a further grave deterioration of relations between the EU and Russia”, said a statement by the EU’s Federica Mogherini. “I call therefore openly upon Russia to use its considerable influence over separatist leaders and to stop any form of military, political or financial support. This would prevent disastrous consequences for all.”

• This article was amended on Sunday 25 January 2015 to correct a mistake in the standfirst and to add updated information to the main body copy.