Russian forces launched a barrage of fatal bombardments across Ukraine early on Monday and President Vladimir Putin vowed even more “severe” retaliation against Kyiv.

The biggest wave of strikes across Ukraine in months killed at least 11 people nationwide and was apparent retaliation for an explosion this weekend that damaged a key bridge linking Russia to the Moscow-annexed Crimean peninsula.

The Ukrainian military said Russian forces had fired more than 80 missiles on cities across the country and that Russia had also used Iranian drones launched from neighbouring Belarus.

“Let there be no doubt,” Putin said in televised comments addressed to his security council, “if attempts at terrorist attacks continue, the response from Russia will be severe.”

Putin's predecessor, Dmitry Medvedev, warned on social media that the strikes — which disrupted water and electricity services across Ukraine — were only “the first episode”.

“We were sleeping when we heard the first explosion. We woke up, went to check and then the second explosion came,” Ksenia Ryazantseva, a 39-year-old language teacher, told AFP.

“We saw the smoke, then the cars, and then we realised we didn't have a window anymore,” she added.

“There's no military target or anything like that here. They're just killing civilians”.

'Demonstration of weakness'

Ukrainian President Volodymyr Zelensky in an address to the nation early on Monday said the morning had been “difficult” and explained that Russian forces had two targets with its barrage of strikes.

“They want panic and chaos and they want to destroy our energy system,” Zelensky said, announcing that Russian bombs had targeted cities including Dnipro and Zaporizhzhia in the centre of the country and Lviv in the east.

“The second target is people,” he said, accusing Moscow's army of launching the strikes with aim of “causing as much damage as possible".

UK Foreign Secretary James Cleverly said that the Russian missile strikes on the Ukrainian capital Kyiv and several other cities were “unacceptable”.

“This is a demonstration of weakness by [Vladimir] Putin, not strength,” he tweeted, adding that he had contacted his Ukrainian counterpart Dmytro Kuleba.

Zelensky said on social media, meanwhile, that he had spoken with the leaders of France and Germany and urged them to “increase pressure” on Russia.

“We discussed the strengthening of our air defence, the need for a tough European and international reaction, as well as increased pressure on the Russian Federation,” Zelensky wrote on Twitter following his call with French President Emmanuel Macron.

In Kyiv, the national police service said that at least five people had been killed and another dozen were wounded.

Ukrainian officials said the central Shevchenkivskyi district of the city was hit and that a university, museums and the philharmonic building had been damaged in the strikes.

One AFP journalist in the city said one of the projectiles landed near a children's playground, and that smoke was rising from a large crater at the impact site.

Several trees and benches nearby were charred from the blast, while several ambulances had arrived in the area.

“If there is no urgent need, it's better not to go to the city today. I am also asking the residents of the suburbs about this — do not go to the capital today.”

Videos posted on social media showed black smoke rising above several areas in the city.

Ukrainian officials including Zelensky urged residents to remain indoors and the mayor of the capital said residents living outside Kyiv should remain outside the city.

In the western city of Lviv, Mayor Andriy Sadovyi said there were disruptions to electricity and hot water services cuts after bombardments that targeted critical infrastructure, including energy facilities.

Ex-Soviet Moldova said several of Russian cruise missiles targeting Ukraine had crossed its airspace and summoned Moscow's envoy to demand an explanation.

“Our thoughts are with the victims of the brutal strikes,” Foreign Minister Nicu Popescu said on Twitter.

Moldova has a small breakaway region, Transnistria, which is armed and supported by Russia.

Crimea bridge attack

Belarusian President Alexander Lukashenko, a close ally of Russian leader Vladimir Putin, meanwhile claimed on Monday that Ukraine was preparing an attack on his country's territory.

The across Ukraine strikes came a day after Moscow blamed Ukraine for the blast on a bridge linking Crimea to Russia, leaving three people dead.

“The authors, perpetrators and sponsors are the Ukrainian secret services,” Russian President Vladimir Putin said of Saturday's Crimea bridge bombing, which he described as a “terrorist act”.

The Kremlin said earlier that Putin would be meeting with members of his security council on Monday.

The blast that hit the bridge sparked celebrations from Ukrainians and others on social media.

But Zelensky, in his nightly address on Saturday, did not directly mention the incident, and officials in Kyiv have made no direct claim of responsibility.

On Saturday, Russia said some road and rail traffic had resumed over the strategic link, a symbol of the Kremlin's 2014 annexation of Crimea.

The 19-kilometre bridge is also a vital supply link between Russia and the annexed Crimean peninsula.

Some military analysts argue that the blast could have a major impact if Moscow sees the need to shift already hard-pressed troops to Crimea from other regions — or if it prompts a rush by residents to leave.