Russia ramped up security on its only bridge to Crimea after a huge blast destroyed sections of it on Saturday.
President Vladimir Putin has now ordered the country’s Federal Security Service (FSB) to oversee the key connector to the occupied peninsula.
The bridge is also a pivotal symbol of Russia’s annexation of Crimea from Ukraine in 2014. The blast killed three people, Russian investigators said.
Officials said work to fix the damaged sections will begin immediately.
Russia’s deputy prime minister ordered the destroyed parts of the bridge to be taken down immediately, and said divers would begin investigating damage below the waterline on Sunday morning, Russian news agencies report.
Hailed by Russian media as “the construction of the century”, the bridge has been crucial to Russia for the movement of military equipment, ammunition and troops into southern Ukraine.
But new satellite images released on Saturday showed smoke and fire near the collapsed areas of the 19km (12-mile) bridge, which was opened with much fanfare four years after Moscow annexed Crimea.
Since it plays a strategic role in the war, Ukrainian authorities have said it is a legitimate target, as they vow to retake the peninsula.
Ukrainian officials responded with thinly-veiled approval to the explosion – but have not indicated that their forces were behind the attack.
President Volodymyr Zelensky acknowledged the incident in his nightly address on Saturday, saying: “Today was not a bad day and mostly sunny on our state’s territory.”
“Unfortunately, it was cloudy in Crimea. Although it was also warm,” he added.
Russian authorities moved swiftly to reopen those parts of the key connector still intact, and said late on Saturday that the bridge has been partially reopened to road and rail traffic.
It is a vital artery in Moscow’s supply chain to the battlefront in its invasion of Ukraine – and to the annexed Crimean territory itself.
The Moscow-appointed governor of Crimea, Sergei Aksyonov, said there was a desire for revenge, but made reassurances that the peninsula still had a month’s worth of fuel and more than two months’ worth of food.
“The situation is manageable – it’s unpleasant, but not fatal,” he said.
Ukrainian official David Arakhamia, parliamentary head of Mr Zelensky’s party, said “Russian illegal construction is starting to fall apart and catch fire.
“The reason is simple: If you build something explosive, then sooner or later it will explode.”
And a Ukrainian MP told the BBC that regardless of who was responsible for the attack, this was a “big Ukrainian victory and very severe and hard loss for Russia.”
“The bridge is not destroyed but damaged, but the image of Putin is destroyed, that is the most important thing,” Oleksiy Goncharenko said.
It is hard to overstate the political, symbolic and strategic significance of the Crimean bridge. Russian officials previously claimed it was well protected from threats from air, land or water – particularly since it is more than 100 miles from Ukrainian-held territory.
A Russian national anti-terrorism committee said the damage was caused by a truck bomb blowing up, which caused seven railway carriages to catch fire. The home of a man from the Krasnodar region of southern Russia is being investigated, it added.
While Ukraine has not linked its armed forces to the explosion, it has targeted Crimea in the past. Last month, Ukraine claimed responsibility for a series of air strikes on Crimea – including an attack on Russia’s Saky military base.
Since the bridge attack on Saturday, Ukraine’s social media has erupted in celebration. Its second-largest bank says it has already issued a new debit card design featuring the collapsed bridge.
In recent weeks, Kyiv’s forces have taken back significant amounts of territory seized by Russia earlier in the war.
Hours after the bridge explosion, Russia appointed a new commander to lead its troops in Ukraine. Sergei Surovikin is a veteran commander known for leading Russian forces in Syria and was accused of overseeing the decimation of the city of Aleppo.
But Russia still controls fast swathes of Ukraine, including the Zaporizhzhia nuclear plant – the biggest in Europe – which has lost all external power and is relying on emergency diesel generators for the energy it needs for reactor cooling, according to the UN nuclear watchdog.
And the nearby city of Zaporizhzhia, in Ukraine’s south-east, saw overnight shelling which killed at least 12 people, according to regional governor Oleksandr Starukh.
A dozen Russian air strikes hit several residential buildings, destroying some and damaging many more, he said.
“There may be more people under the rubble. A rescue operation is under way at the scene. Eight people have already been rescued,” he said on Telegram.
Earlier, officials said 17 people had been killed in the shelling.
