Kiev/Moscow, 18 July 2023 (dpa/MIA) - Russian President Vladimir Putin has threatened military retaliation against Ukraine after accusing it of attacking the bridge to the Black Sea peninsula of Crimea.

"Naturally, Russia's response will follow. The Defence Ministry is working on relevant proposals," Putin said at a meeting of the Russian leadership in Moscow on Monday evening, as reported by the state news agency TASS.

"What happened is yet another terrorist act of the Kiev regime," Putin said.

The Russian president demanded that security measures at the bridge from the Russian mainland to the Ukrainian peninsula annexed in 2014 be strengthened. He said it was the second attack on the "strategic, important transportation structure" since October 2022.

Putin denied that Russia was using the bridge for military transport in the war against Ukraine.

According to Russia, unmanned remote-controlled boats had detonated explosives at the structure on Monday morning. As a result, part of the roadway for cars collapsed, as photos showed.

The foundation of the bridge was not damaged, according to Deputy Prime Minister Marat Khusnullin, who said only one of the two lanes was being used. According to the Russian government, car traffic resumed with restrictions on Monday night.

Rail traffic over the bridge had already resumed, with a delay of around five hours.

The incident, described earlier on Monday by the local administration as an "emergency," caused traffic to be halted on the heavily-used crossing.

The bridge spans a 19-kilometre stretch over the Kerch Strait and is the only link that does not run through the war zone.

The bridge was hit by overwater drones early on Monday morning, the Russian authorities reported.

There was no official confirmation from Kiev of any involvement in the incident, but the Ukrainian secret service SBU commented on the apparent explosion.

"Once again the bridge has gone 'to sleep'," the agency said. The SBU had admitted involvement in a previous attack on the bridge in October, which left a section of it severely damaged.

According to Russian authorities, two people were killed in the blast and their teenage daughter was injured.

Kiev has stated its intention to take back Crimea, which Russia annexed in 2014 in violation of international law.

Ukraine has been fighting off Russia's full-scale invasion of the country since February 2022.

Late Monday, the Ukrainian military reports heavy Russian attacks in the Kupyansk area of the eastern Kharkiv region.

The Russian army is also sending additional forces, mainly airborne troops, to the town of Bakhmut, Ukrainian army commander of the army, Oleksandr Syrskyi, added.

The Ukrainian troops had cleared out of Bakhmut several weeks ago after months of fighting. However, they are advancing again in their large-scale offensive to areas north and south of the city, according to Kiev.