KHARKIV, Ukraine (AP) — Russian authorities said that a truck bomb on Saturday caused a fire and the collapse of a section of a bridge linking Russia-annexed Crimea with Russia — a key supply artery for Moscow’s faltering war effort in southern Ukraine.

The attack on the bridge comes a day after Russian President Vladimir Putin turned 70, dealing him a humiliating blow that could lead him to up the ante in his war on Ukraine.

Russia’s National Anti-Terrorism Committee said that the truck bomb caused seven railway cars carrying fuel to catch fire, resulting in a “partial collapse of two sections of the bridge.” The committee didn’t immediately apportion blame.

The Crimean Peninsula holds symbolic value for Russia and is key to sustaining its military operations in the south. If the bridge is made inoperable, it would make it significantly more challenging to ferry supplies to the peninsula. While Russia seized the areas north of Crimea early during the invasion and built a land corridor to it along the Sea of Azov, Ukraine is pressing a counteroffensive to reclaim them.

The bridge has train and automobile sections. Russia’s National Anti-Terrorism Committee specified that the explosion and fire led to the collapse of the two sections of one of the two links of the automobile bridge, while another link was intact.

Authorities have suspended commuter train traffic across the bridge until further notice. Putin was informed about the explosion and he ordered the creation of a government panel to deal with the emergency.

The 19-kilometer (12-mile) bridge across the Kerch Strait linking the Black Sea and the Sea of Azov is the longest in Europe. It has provided an essential link to the Crimean Peninsula, which Russia annexed from Ukraine in 2014. Ukrainian officials have repeatedly threatened to strike the bridge.

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

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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.

In August, Russia suffered a series of explosions at an airbase and munitions depot in Crimea, which underlined its vulnerability.

The truck bomb on the bridge 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 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.

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Adam Schreck reported from Kyiv. Francisco Seco contributed to this report from Kharkiv.

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Follow the AP’s coverage of the war at https://apnews.com/hub/russia-ukraine