Rockets slammed into a high-security prison in the rebel-held city of Donetsk, igniting a riot that allowed more than 100 prisoners to flee, authorities in eastern Ukraine said.
Donetsk city council spokesman Maxim Rovinsky said a direct rocket hit killed at least one inmate and left three others severely wounded. In the chaos, he said 106 prisoners escaped, included some jailed for murder, robbery and rape.
In the past week Ukrainian government forces have intensified their military operations and surrounded Donetsk, the largest city in rebel-held eastern Ukraine.
Exchanges of rocket fire and deaths from shelling have become a feature of daily life and hundreds of thousands have chosen to flee.
The prison break became possible after a substation providing the building with electricity was damaged, disabling the facility’s alarm system.
‘‘Extremely dangerous prisoners are now free. It is hard to know the extent of threat this poses to the city, which is flooded with weapons,’’ Rovinsky said.
Officials with Ukraine’s state penitentiary service said later on Monday that 34 prisoners had returned to the jail. It was not immediately possible to verify that claim.
Both Ukrainian government forces and the pro-Russian rebels who want independence for their eastern region have deployed heavy and often imprecise weapons in the battle that began in April. Apartments and other civilian buildings have frequently been hit, adding to the mounting death toll among civilians.
Rovinsky said Monday at least 10 homes, shops and garages were hit by overnight rockets. He added that 20,000 people had no electricity in Donetsk and an estimated 400,000 have fled the city, which had a pre-war population of 1 million. Many shops have closed and supplies are dwindling at the few still open.
The Ukrainians army’s strategy has focused on encircling Donetsk and nearby rebel towns and breaking off road links with other separatist towns and villages further east, closer to the Russian border.
Many of those in Russian-speaking eastern Ukraine distrust the new central government in Kiev, which came to power after the February ouster of former President Viktor Yanukovych, whose power base was in eastern Ukraine.
On Sunday Ukraine's military demanded that pro-Russian rebels surrender and dismissed their offer of a cease-fire, as lawmakers prepared to consider new sanctions that may cut Russian shipments of natural gas to Europe.
"If there is an initiative, it should be implemented by practical means, not only with words — by raising white flags and putting down weapons," Andriy Lysenko, a spokesman for the country's military, told reporters in Kiev. "In that case no one will shoot at them."
Ukraine is trying to dislodge separatists from strongholds in Donetsk and Luhansk as Russia raises the pressure on its western neighbour to halt the campaign and allow immediate assistance.
Ukrainian government forces are preparing for the final stage of recapturing the city of Donetsk from pro-Russian separatist rebels after making significant gains that have divided rebel forces, a military spokesman said on Monday.
The spokesman, Andriy Lysenko, said Kiev’s forces had now cut Donetsk off from the other main rebel-held city of Luhansk on the border with Russia.
‘‘The forces of the ’anti-terrorist operation’ are preparing for the final stage of liberating Donetsk. Our forces have completely cut Donetsk off from Luhansk. We are working for liberating both towns but it’s better to liberate Donetsk first — it is more important,’’ Lysenko said.
Russian President Vladimir Putin, who has been blamed by Ukraine and its US and European allies of stoking the conflict, has said the fighting is creating a humanitarian disaster and offered to provide aid.
As Ukraine wrestled with Russia over a military standoff, Ukrainian lawmakers prepared to vote Tuesday on a sanctions bill that could block the transit of Russian oil and gas supplies to Europe. The cabinet has approved the measure.
Ukraine no longer receives gas from Russia though acts as a conduit for its neighbor's European shipments, and a ban could be "complete or partial," Prime Minister Arseniy Yatsenuyuk said last week. It also may ban Russian planes from its airspace and cut defence-industry cooperation.
Russia has responded to sanctions by banning food imports from Ukraine, the US, the European Union and other countries.
If new sanctions against Russia are approved, "we will retaliate," Putin spokesman Dmitry Peskov said.
As the army pushed toward Donetsk, Ukraine's military reported more desertions among militants, and said the town of Panteleymonivka was cleared of rebels, according to a posting on its Facebook page.
Government troops cut off regions of Donetsk and Luhansk from one another, threatening resupply routes. Insurgents dug in near the town of Illovaysk, armed with tanks, Grad missiles and armoured vehicles, and the military is preparing to storm the area, according to the military.
A rebel leader had broached the possibility of a truce during the weekend, saying in a statement that militants will continue fighting if the government doesn't end its offensive. The Defense Ministry in Kiev said the army continued to tighten its encirclement of Donetsk, biggest city in the conflict zone.
"A cease-fire isn't only possible; it's urgently needed," Russian Foreign Minister Sergei Lavrov told reporters in Sochi on Sunday. "Hospitals can't function, there's not enough medications. That amounts to the most severe humanitarian situation."
As of noon local time on Sunday, the atmosphere was "extremely tense" in Donetsk, a city of 1 million people before the conflict flared in mid-April, the council said in a statement, adding that shells were heard hitting most areas. More than 10,000 residents had no electricity late on Sunday after 40 substations were damaged by artillery, it said.
Luhansk hasn't had power, water or phone service for more than a week, according to local authorities.
Russia is negotiating with Ukraine, the Red Cross and humanitarian groups run by the United Nations about providing urgent assistance, Lavrov said. "I'm certain we'll be able to agree on delivering this aid as soon as possible to those who need it most," he said.
Valeriy Chaly, deputy chief of Ukrainian President Petro Poroshenko's administration, said a column of Russian soldiers and army equipment stopped before crossing the border after leaders asked the US, Russia and the Red Cross to intervene. Chaly, in a statement Saturday on Poroshenko's website, called the dispatching of the convoy a "very serious provocation."
The Kremlin denied the claim.
Ukrainian officials and their allies had predicted Putin would cloak an incursion of Russian troops into those areas as a peacekeeping effort.
"There were no attempts made to penetrate" Ukrainian territory "by Russian forces," said Putin's spokesman Peskov. "That's why we find it difficult to understand what was meant by the Ukrainian side."
The prospect of a Kremlin intervention spurred talks among world leaders who have imposed economic sanctions in a bid to force Putin to de-escalate tensions.
US President Barack Obama and German Chancellor Angela Merkel "agreed that any Russian intervention in Ukraine, even under purported 'humanitarian' auspices, without the formal, express consent and authorization of the government of Ukraine is unacceptable, violates international law, and will provoke additional consequences," according to a White House statement on Saturday.
The militants are "in panic" as government troops tighten their encirclement of insurgents around Donetsk, Leonid Matyukhin, a spokesman for the Ukrainian Defense Ministry, said in a statement on Facebook.
The army inflicted losses and destroyed vehicles by firing on rebel bases, while insurgents struck back by attacking Ukrainian checkpoints, with artillery fire hitting Ukraine from Russia, he said.