By Max Hunder and Jonathan Landay
Thick smoke rose from central Kyiv after the city was rocked by several loud blasts, witnesses said. It was not immediately clear what caused the explosions and there were no immediate reports of casualties.
Putin said on Sunday that the blast a day earlier on the bridge over the Kerch Strait, a major supply route for Moscow's forces in southern Ukraine, 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.
Ukraine has not claimed responsibility for the blast but senior Russian officials demanded a swift response from the Kremlin before a meeting of Putin's security council on Monday.
Security Council deputy chairperson Dmitry Medvedev said 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.
The Kerch bridge is a vital artery for the port of Sevastopol, where the Russian Black Sea fleet is based, and an imposing symbol of Russia's 2014 annexation of the Crimean peninsula.
Putin opened the 19km road and rail span linking Crimea to Russia, with great fanfare in 2018.
The damage to the bridge came amid battlefield defeats for Russia and initial reports from Ukrainian officials of a mass burial site discovered in the recently liberated eastern town of Lyman.
Putin's anger over the suspected attack also coincided with growing concerns that Moscow could resort to nuclear weapons, after Putin repeatedly cautioned the West that any attack on Russia could provoke a nuclear response.
Alexander Bastrykin, the head of Russia's Investigative Committee, said on Sunday that 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.
Oleksandr Kovalenko, a military analyst and head of the website Information Resistance, told Espreso TV website, a digital broadcaster well known in Ukraine, that Russia might intensify attacks on civilian targets after the explosion on the Crimea bridge.
"This probably means missile attacks on border areas – Sumyand Chernihiv regions. It could also mean using missiles and (Iranian-made) Shahed-136 drones to hit even deeper into Ukrainian territory," he said.
Images showed part of the bridge's road blown away, although rail services and partial road traffic resumed.
The Russian transport ministry, quoted by RIA news agency,said nearly 1 500 people and 162 heavy cargoes had travelled by ferry across the Kerch Strait since the explosion.
Russia's defence ministry said on Saturday that its forces in southern Ukraine could be "fully supplied" through land and sea routes.
FRESH ATTACK ON ZAPORIZHZHIA
In south-eastern Ukraine, Russian shelling overnight destroyed an apartment building in the city of Zaporizhzhia, regional Governor Oleksandr Starukh said early on Monday. At least one person died and five were injured in the attack, a city official said.
The pre-dawn strikes were the third such attack against the region in four days. A strike on an apartment in the city on Sunday killed at least 13 people and injured 87 others, including 10 children, Ukrainian officials said.
Ukraine's general staff said seven anti-aircraft guided missiles were used in the latest attack.
Russian aircraft launched at least 12 missiles in Sunday's attack, partially destroying a nine-storey apartment block, levelling five other residential buildings and damaging many more, Starukh said on state-run television.
Ukrainian President Volodymyr Zelenskiy condemned Sunday's 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.
Zaporizhzhia city, about 52km from a Russian-held nuclear power plant, has been under frequent shelling in recent weeks, with 19 people killed on Thursday.
Russia denies targeting civilians and Vladimir Rogov, an official in the Russian-installed administration in Zaporizhzhia, said Ukrainian forces had shelled the city for"propaganda purposes".
Most of the Zaporizhzhia region, including the nuclear plant, have been under Russian control since the early days of Russia's invasion in February. The capital of the region, Zaporizhzhia city, remains under Ukrainian control.
Russian troops were continuing to focus their efforts on the strategically important eastern town of Bakhmut, having advanced up to 2km towards the town over the past week, a British intelligence update said on Monday. Bakhmut sits on a main road in the industrial Donbas region, which Moscow says it intends to capture.
US TO CONTINUE ARMING UKRAINE
On Sunday, the White House declined to comment on the bridge blast but said the US would continue to arm Ukraine.
Kyiv demands that Russian forces leave the Black Sea peninsula of Crimea, as well as Ukrainian territory they have seized in the invasion Putin launched in February.
Ukraine had recaptured more than 1 170km² of land in its southern Kherson region since launching its counter-attack in late August, a military spokesperson said on Sunday.