Three people died after a truck exploded on a bridge linking Moscow-annexed Crimea to Russia on Saturday.

Russian President Vladimir Putin has issued a decree ordering the FSB secret service to tighten controls over the Crimean bridge that was damaged by a huge blast earlier on Saturday.

"The FSB will be given powers to organize and coordinate protective measures for the transport route across the Kerch Strait, for the Russian Federation's power bridge to the Crimean peninsula and the gas pipeline from the Krasnodar Territory Crimea," the decree says.

It is the Kremlin's first measure after the blast, which appeared to have been caused in an attack on the structure built by Moscow following its annexation of Crimea.

Russian investigators said three people had been killed. Two bodies — a man and a woman — were pulled out of the water after the bridge had partially collapsed.

Their identities were still to be established, but they were likely passengers in a car driving near the exploded truck, Moscow said.

The authorities also said they had identified the owner of the truck as a resident of Russia's southern Krasnodar region, saying his home was being searched.

Russia said the blast — which happened just after 6:00 am local time — had set ablaze seven oil tankers transported by train and collapsed two car lanes of the giant road and rail structure.

RIA-Novosti and the Tass news agency quoted local Russian official Oleg Kryuchkov as saying an object thought to be a fuel storage tank caught fire and that traffic has been stopped on the bridge. He said the span's "navigable arches" weren't damaged and that work was ongoing to extinguish the blaze.

The fire occurred hours after explosions rocked the eastern Ukrainian city of Kharkiv early Saturday, sending towering plumes of smoke into the sky and triggering a series of secondary explosions.

Kharkiv Mayor Ihor Terekhov said on Telegram that the early-morning explosions were the result of missile strikes in the center of the city. He said that the blasts sparked fires at one of the city’s medical institutions and a nonresidential building. There were no immediate reports of casualties.

The blasts came hours after Russia concentrated attacks in its increasingly troubled invasion of Ukraine on areas it illegally annexed, while the death toll from earlier missile strikes on apartment buildings in the southern city of Zaporizhzhia rose to 14.

On Friday, the Norwegian Nobel Committee awarded the Nobel Peace Prize to human rights organizations in his Russia and Ukraine, and to an activist jailed in Belarus, an ally of Moscow.

Berit Reiss-Andersen, the committee’s chair, said the honor went to "three outstanding champions of human rights, democracy and peaceful coexistence," though it was widely seen as a rebuke to Russian President Vladimir Putin and his conduct of Europe’s worst armed conflict since World War II.

Putin signed documents on Wednesday to illegally claim four regions of Ukraine as Russian territory, including the Zaporizhzhia region that is home to Europe’s largest nuclear power plant, whose reactors were shut down last month.

That move was foreshadowed by Russia’s annexation of Crimea in March 2014, which was carried out after Moscow alleged residents of the peninsula had voted to join with Russia. That move was widely condemned, and prompted sanctions from the U.S. and the European Union.

The 19-kilometer (12-mile) bridge across the Kerch Strait links Russia’s Taman Peninsula with Crimea.

Russia opened the first part of the span to car traffic in May 2018. The parallel bridge for rail traffic opened the following year.

The $3.6 billion project is a tangible symbol of Moscow’s claims on Crimea. It was Russia’s only land link to the peninsula until Russian forces seized more Ukrainian territory on the northern end of the Sea of Azov in heavy fighting, particularly around the city of Mariupol, earlier this year.