Massive explosions shook the Ukrainian capital and other cities during the morning rush hour on Monday, as Russia responded to a truck bomb attack on the bridge between mainland Russia and Crimea at the weekend.
Kyiv police say at least five people have been killed and 12 wounded.
In televised remarks, Russian President Vladimir Putin said Moscow had launched long-range missile attacks against Ukraine's energy, military and communications infrastructure in retaliation for an attack on a vital bridge linking Russia to the annexed Crimean peninsula over the weekend.
Putin said Ukraine had carried out "terrorist acts" against Russia and pledged to react forcefully if they continued.
"It is obvious that the Ukrainian secret services ordered, organised and carried out the terrorist attack aimed at destroying Russia's critical civilian infrastructure," Putin said of the bridge explosion.
Ukrainian officials were exultant after the blast but Kyiv has not claimed responsibility.
"Through its actions, the Kyiv regime has put itself on a par with the most odious of international terrorist groups. It is simply impossible to leave crimes of this kind unanswered," Putin said, in opening remarks at a meeting of his powerful Security Council.
The attacks were the most intense to hit the Ukrainian capital since the early days of the war and sent residents fleeing for bomb shelters and thick smoke billowing skywards.
Explosions were also reported in Lviv, Ternopil and Zhytomyr in Ukraine's west, and in Dnipro in central Ukraine.
At one of Kyiv's busiest road junctions, a massive crater had been blown in the intersection. Cars were blown out, buildings were damaged and emergency workers were on the scene. Two cars and a van near the crater were completely wrecked, blacked and pitted from shrapnel.
Windows had been blown out of buildings at Kyiv's main Taras Shevchenko University. National Guard troops in full combat gear and carrying assault rifles were lined up outside an education union building.
"The capital is under attack from Russian terrorists! The missiles hit objects in the city centre (in the Shevchenkivskyi district) and in the Solomyanskyi district. The air raids sirens are going off, and therefore the threat, continues," mayor Vitali Klitschko posted on social media.
"The central streets of Kyiv have been blocked by law enforcement officers, rescue services are working."
A spokesperson for the state emergency services said there were dead and wounded, though provided no immediate figures.
Putin said on Sunday that the blast which damaged the only bridge over the Kerch Strait to the Crimea peninsula, was "an act of terrorism aimed at destroying critically important civilian infrastructure".
"This was devised, carried out and ordered by the Ukrainian special services," he said in a video on the Kremlin's Telegram channel.
Senior Russian officials had demanded a swift response from the Kremlin ahead of the Security Council today.
Russian Security Council deputy chairman Dmitry Medvedev said ahead of the meeting that Russia should kill the "terrorists" responsible for the attack.
"Russia can only respond to this crime by directly killing terrorists, as is the custom elsewhere in the world. This is what Russian citizens expect," he was quoted as saying by state news agency Tass.
Alexander Bastrykin, the head of Russia's Investigative Committee, said on Sunday a vehicle had exploded on the bridge causing a fire.
The vehicle had travelled through Bulgaria, Georgia, Armenia, North Ossetia and Russia's Krasnodar region before reaching the bridge, he said. Among those who helped Ukrainian special services prepare the attack were "citizens of Russia and foreign countries," Bastrykin added in the video on the Kremlin's Telegram channel.
Russia's defence ministry said on Saturday its forces in southern Ukraine could be "fully supplied" through existing land and sea routes.
Fresh attack on Zaporizhzhia
In southeastern Ukraine, Russian shelling overnight destroyed another apartment building in the city of Zaporizhzhia, regional Governor Oleksandr Starukh said early on Monday. At least one person died and five where injured in the attack, a city official said.
The pre-dawn strikes were the third Russian missile attack against apartment buildings in the city in four days. The city, which Russian forces never captured, is the capital of one of four partially occupied regions Russia claims to have annexed this month.
A strike on an apartment in the city on Sunday killed at least 13 people and injured 87 others, including 10 children, according to Ukrainian officials. Ukrainian President Volodymyr Zelensky condemned that attack as "absolute evil".
"This was a deliberate hit. Whoever gave the order and whoever carried it out knew what they were targeting," he said in a video address.
Russia denies targeting civilians. Vladimir Rogov, an official in the Russian-installed administration in Zaporizhzhia, said without evidence that Ukrainian forces had shelled the city for "propaganda purposes".
Russia has faced major setbacks on the battlefield since the start of September, with Ukrainian forces bursting through the front lines and recapturing territory in the northeast and the south.
Putin responded to the losses by ordering a mobilisation of hundreds of thousands of reservists, proclaiming the annexation of occupied territory and threatening repeatedly to use nuclear weapons.
Russian troops are focusing their efforts on the eastern town of Bakhmut, having advanced up to 2km towards the town over the last week, a British intelligence update said on Monday.
- Reuters