Russia has said three people were killed after a truck exploded on its bridge linking Crimea - a symbol of its annexation of the peninsula - without immediately blaming Ukraine.
On the same day, after Moscow suffered a series of setbacks on the battlefield that triggered unprecedented criticism of its army at home, Russia appointed a new general to lead its Ukraine offensive.
The blast ripped through the 19km bridge more than seven months into Moscow's Ukraine offensive, although local authorities said it had reopened to motor traffic with vehicles subject to stringent screening.
Local officials said later that it had reopened to motor traffic with vehicles subject to stringent screening.
Shortly after, Grand Service Express, which operates rail services there, said the first trains had left the peninsula for Moscow and St Petersburg.
The blast aroused intense excitement and speculation from Ukrainians and others on social media, but Ukrainian President Volodymyr Zelensky made no direct mention of it in his nightly address, and officials made no claim of responsibility.
Dramatic social media footage showed the bridge on fire with parts plunging into the water.
We need your consent to load this rte-player contentWe use rte-player to manage extra content that can set cookies on your device and collect data about your activity. Please review their details and accept them to load the content.Manage Preferences
Russian investigators said three people were killed and that two bodies - a man and a woman - were pulled out of the water after the bridge had partially collapsed.
They were likely to be passengers of a car that was driving near the exploded truck and that their identities were being established, Russia said.
It had also identified the owner of the truck as a resident of Russia's southern Krasnodar region, saying his place of residence was being searched.
Russia said the blast - which occurred just after 6am local time (3am Irish time) - set ablaze seven oil tankers transported by train and collapsed two car lanes of the giant road and rail structure.
The bridge is logistically crucial for Russia, a vital transport link for carrying military equipment to Russian soldiers fighting in Ukraine.
It is also hugely symbolic.
President Vladimir Putin personally inaugurated the bridge in 2018 - even driving a truck across it - and Russia had maintained the crossing was safe despite the fighting.
The bridge, personally inaugurated by President Vladimir Putin in 2018, is a vital transport link for carrying military equipment to Russian soldiers fighting in Ukraine.
While some in Moscow hinted at Ukrainian "terrorism", state media continued to call it an "emergency situation."
Ukraine's presidential advisor Mykhailo Podolyak earlier took to Twitter posting a picture of a long section of the bridge half-submerged.
"Crimea, the bridge, the beginning," he wrote.
"Everything illegal must be destroyed, everything stolen must be returned to Ukraine, everything occupied by Russia must be expelled."
The Ukrainian post office announced it was preparing to print stamps showing the "Crimean bridge - or more precisely, what remains of it".
The Kremlin's spokesman said Mr Putin had ordered a commission to be set up to look into the blast on the bridge which is hugely symbolic and logistically crucial for Moscow.
Officials in Russia stopped short of blaming Ukraine.
But a Russian-installed official in Crimea pointed the finger at "Ukrainian vandals." Another in the neighbouring Kherson region said repairs could "take two months".
And the spokeswoman of Russia's foreign ministry said that Ukraine's reaction to the blasts showed its "terrorist nature."
Calls for retaliation
Some officials in Russia and in Russian-occupied Ukraine called for retaliation.
"There is an undisguised terrorist war against us," Russian ruling party deputy Oleg Morozov told the RIA Novosti news agency.
A Russian-installed official in the occupied Ukrainian Kherson region, Kirill Stremousov, said: "Everyone is waiting for a retaliatory strike and it is likely to come."
There have been several explosions at Russian military installations in the Crimean peninsula.
If it is established that Ukraine was behind the latest blast, alarm bells may sound with the bridge so far from the frontline.
Authorities in Crimea appeared to downplay the blasts and tried to calm fears of food and fuel shortages in Crimea, which is fully reliant on the Russian mainland since Moscow annexed it in 2014.
At around 5pm (3pm Irish time), the Russian-backed head of the peninsula, Sergei Askyonov, said car traffic had resumed on the bridge but that all vehicles were being inspected.
"Road traffic has begun on the Crimea bridge," he said on Telegram.
The blasts come after Ukraine's recent lightning territorial gains in the east and south that have undermined the Kremlin's claim that it annexed Donetsk, neighbouring Luhansk and the southern regions of Zaporizhzhia and Kherson.
Moscow appoints new general
After several weeks of crushing military defeats, Moscow on Saturday announced that a new general - Sergei Surovikin - would take over its forces in Ukraine.
The decision - made public in an unusual move - comes after the setbacks on the battlefield led to growing discontent among the elite towards the army's leadership.
This month, Chechen leader Ramzan Kadyrov had called for a top general to be fired in Ukraine after Russian forces lost control of the key city of Lyman.
Mr Surovikin previously led Russia's forces in southern Ukraine. He has combat experience in the 1990s conflicts in Tajikistan and Chechnya, as well as, more recently, in Syria.
Also on Saturday, the governor of Russia's Belgorod region that borders Ukraine said Kyiv's forces had fired at a Russian border village, injuring a teenage girl.
But Russian forces had made some gains in eastern Ukraine this week.
On Friday, Moscow said its forces had captured ground in Donetsk in east Ukraine, their first claim of new gains since a Kyiv counter-offensive rattled Moscow's military campaign.
The Donetsk region, which has been partially controlled by Kremlin-backed separatists for years, is a key prize for Russian forces, which sent troops to Ukraine in February.
Zaporizhzhia plant down to diesel generators
Overnight shelling cut the power line supplying Ukraine's Russian-occupied Zaporizhzhia nuclear plant, forcing it to switch to emergency diesel generators, Ukraine's state nuclear company and the UN atomic watchdog said.
Russia and Ukraine have blamed each other for shelling at the site of Europe's biggest nuclear plant that has damaged buildings and threatened a catastrophic nuclear accident. The International Atomic Energy Agency is pushing for a protection zone to be set up to prevent further shelling.
Even though Zaporizhzhia's six reactors are shut down the nuclear fuel in them still needs cooling to prevent a nuclear meltdown. That requires a constant supply of electricity.
"The resumption of shelling, hitting the plant's sole source of external power, is tremendously irresponsible. The Zaporizhzhya Nuclear Power Plant must be protected," the IAEA quoted its chief Rafael Grossi as saying in a statement.
The IAEA confirmed an earlier statement by Ukrainian nuclear regulator Energoatom that said the plant had switched to its diesel generators after shelling at around 1am cut the main 750 kilovolt line supplying external power to the plant.
"All the plant's safety systems continue to receive power and are operating normally, the IAEA experts (stationed at Zaporizhzhia) were informed by senior Ukrainian operating staff," the IAEA said.
Mr Grossi has been in talks with Russia and Ukraine on setting up a protection zone around the plant, though he has declined to say what that would involve exactly or how it would be enforced or monitored.
He was in Kyiv on Thursday and is due to go to Russia early next week.
"I will soon travel to the Russian Federation, and then return to Ukraine, to agree on a nuclear safety and security protection zone around the plant. This is an absolute and urgent imperative," the IAEA quoted Mr Grossi as saying.