Russian President Vladimir Putin has signed a decree tightening security for a bridge linking the Crimean Peninsula with Russia after an explosion caused part of it to collapse.

Damage to the bridge has hampered an important supply route for the Kremlin’s war in southern Ukraine and represents a strike on a symbol of Russian power in the region.

Nobody has claimed responsibility for the blast, which killed three people.

It comes as a search and rescue operation is underway in the Ukrainian city of Zaporizhzhia after Russian shelling hit apartment buildings, killing at least 12 people in the early hours of Sunday.

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Russian divers will examine the damage caused to the bridge over the Kerch Strait on Sunday.

The National Anti-Terrorism Committee said a truck bomb caused seven railway cars carrying fuel to catch fire, resulting in the “partial collapse of two sections of the bridge”.

A man and a woman riding in a vehicle on the bridge were killed, Russia’s Investigative Committee said. It did not say who the third victim was.

All vehicles crossing the bridge are supposed to undergo state-of-the-art checks for explosives.

The truck that exploded was owned by a resident of the Krasnodar region in southern Russia, the Investigative Committee said. It said his home was searched and experts were investigating the truck’s route.

Russian authorities have said the attack was a “terrorist action” carried out by Ukraine.

Train and vehicle traffic over the bridge was temporarily suspended though vehicle traffic resumed on Saturday afternoon on one of the two links that remained intact, said Crimea’s Russian-backed leader Sergey Aksyonov.

Rail traffic was resuming slowly, with two passenger trains leaving the Crimean cities of Sevastopol and Simferopol and heading towards the bridge on Saturday evening.

Mr Putin has put Russia’s federal security service, the FSB, in charge of security for the bridge and energy infrastructure between Crimea and Russia.

Hours after the explosion Russia’s defence ministry announced the air force chief, General Sergei Surovikin, would now command Russian troops in Ukraine. He has previously led Russian forces in Syria and has been accused of overseeing a bombardment that destroyed much of Aleppo.

The 12-mile (19km) Kerch Bridge, which sits on a strait between the Black Sea and the Sea of Azov, is vital for sustaining Russia’s military supply lines in southern Ukraine.

Mr Putin himself presided over the opening of the £3.5bn bridge, the longest in Europe, in 2018.

Ukrainian President Volodymyr Zelenskyy indirectly acknowledged the attack on the bridge but did not address its cause.

Meanwhile, a search and rescue operation is underway in the city of Zaporizhzhia.

Overnight, Russian shells hit apartment buildings, with at least 12 people killed.

Since then, however, the office of the General Staff of Ukraine’s Armed Forces has said “dozens” were killed or injured.

The city is in the Ukrainian-controlled part of a region annexed by Mr Putin last week – a move not recognised by other world powers.

City council secretary Anatoliy Kurtev said at least five private houses were destroyed and around 40 were damaged.