An explosion Saturday caused the partial collapse of a bridge linking the Crimean Peninsula with Russia, damaging an important supply artery for the Kremlin's faltering war effort in southern Ukraine and hitting a towering symbol of Russian power in the region.

Nobody immediately claimed responsibility for the blast, which killed three people. The speaker of the Russian-backed regional parliament in Crimea accused Ukraine, but Moscow didn't apportion blame. Ukrainian officials have repeatedly threatened to strike the bridge, and some lauded the destruction on Saturday. But Kyiv stopped short of claiming responsibility.

The explosion, which Russian authorities said was caused by a truck bomb, risked a sharp escalation in Russia's eight-month war, with some Russian lawmakers calling for President Vladimir Putin to declare a "counterterrorism operation," shedding the term "special military operation" that had downplayed the scope of fighting to ordinary Russians.

Putin signed a decree late Saturday tightening security for the bridge and for energy infrastructure between Crimea and Russia, and put Russia's federal security service, the FSB, in charge of the effort.

Hours after the explosion, Russia's Defense Ministry announced that the air force chief, Gen. Sergei Surovikin, would now command all Russian troops in Ukraine. Surovikin, who this summer was placed in charge of troops in southern Ukraine, had led Russian forces in Syria and was accused of overseeing a bombardment that destroyed much of Aleppo.

Moscow, however, continues to suffer battlefield losses.

On Saturday, a Kremlin-backed official in Ukraine's Kherson region announced a partial evacuation of civilians from the southern province, one of four illegally annexed by Moscow last week. Kirill Stremousov told Russia's state-run RIA Novosti agency that young children and the elderly could be relocated because Kherson was getting "ready for a difficult period."

The 19-kilometer (12-mile) Kerch Bridge, on a strait between the Black Sea and the Sea of Azov, is a symbol of Moscow's claims on Crimea and an essential link to the peninsula, which Russia annexed from Ukraine in 2014. The $3.6 billion bridge, the longest in Europe, is vital to sustaining Russia's military operations in southern Ukraine. Putin himself presided over the bridge's opening in 2018.

The attack on it "will have a further sapping effort on Russian morale, (and) will give an extra boost to Ukraine's," said James Nixey of Chatham House, a think tank in London. "Conceivably the Russians can rebuild it, but they can't defend it while losing a war."

Ukrainian President Volodymyr Zelenskyy, in a video address, indirectly acknowledged the bridge attack but did not address its cause.

"Today was not a bad day and mostly sunny on our state's territory," he said. "Unfortunately, it was cloudy in Crimea. Although it was also warm."

Zelenskyy said Ukraine wants a future "without occupiers. Throughout our territory, in particular in Crimea."

Zelenskyy also said Ukrainian forces advanced or held the line in the east and south, but acknowledged "very, very difficult, very tough fighting" around the city of Bakhmut in the eastern Donetsk region, where Russian forces have claimed recent gains.

Russia's 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 couple riding in a vehicle on the bridge were killed, Russia's Investigative Committee said. It didn't 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, adding that the man's home was searched and experts were looking at the truck's route.

Train and automobile traffic over the bridge was temporarily suspended. Automobile traffic resumed Saturday afternoon on one of the two links that remained intact, with the flow alternating in each direction, said Crimea's Russia-backed leader, Sergey Aksyonov.

Rail traffic was resuming slowly. Two passenger trains left the Crimean cities of Sevastopol and Simferopol and headed toward the bridge Saturday evening. Passenger ferry links between Crimea and the Russian mainland were being relaunched Sunday.

While Russia seized areas north of Crimea early in its invasion of Ukraine and built a land corridor to it along the Sea of Azov, Ukraine is pressing a counteroffensive to reclaim that territory.

The Russian Defense Ministry said its troops in the south were receiving necessary supplies through that corridor and by sea.

Russian war bloggers responded to the bridge attack with fury, urging Moscow to retaliate by striking Ukrainian civilian infrastructure. Putin ordered the creation of a government panel to deal with the emergency. Gennady Zyuganov, head of the Russian Communist Party, said the "terror attack" should serve as a wake-up call. "The special operation must be turned into a counterterrorist operation," he declared.

Leonid Slutsky, head of the foreign affairs committee in the Russian parliament's lower house, said "consequences will be imminent" if Ukraine was responsible. And Sergei Mironov, leader of the Just Russia faction, said Russia should respond by attacking key Ukrainian infrastructure.

Such statements may herald a decision by Putin to declare a counterterrorism operation.

The parliamentary leader of Zelenskyy's party cast the explosion as a consequence of Moscow's takeover of Crimea.

"Russian illegal construction is starting to fall apart and catch fire. The reason is simple: If you build something explosive, then sooner or later it will explode," said David Arakhamia of the Servant of the People party.

The Ukrainian postal service announced it would issue stamps commemorating the blast, as it did after the sinking of the Moskva, a Russian flagship cruiser, by a Ukrainian strike.

The secretary of Ukraine's National Security and Defense Council, Oleksiy Danilov, tweeted a video with the Kerch Bridge on fire and Marilyn Monroe singing her "Happy Birthday Mr. President" song. Putin turned 70 on Friday.

In Moscow, Foreign Ministry spokeswoman Maria Zakharova said "the reaction of the Kyiv regime to the destruction of civilian infrastructure shows its terrorist nature."

The Crimean Peninsula is a popular destination for Russian tourists and home to a Russian naval base. A Russian tourist association estimated that 50,000 tourists were in Crimea on Saturday.

Elsewhere, the U.N. nuclear watchdog said Ukraine's Zaporizhzhia nuclear power plant has lost its last remaining external power source as a result of renewed shelling and is now relying on emergency diesel generators.

Ukrainian authorities were also just beginning to sift through the wreckage of the devastated city of Lyman in eastern Ukraine, assessing the humanitarian toll and possible war crimes after a months-long Russian occupation.

"Some people died in their houses, some people died in the streets, and the bodies are now being sent to experts for examination," said Mark Tkachenko of the Kramatorsk district police.

Explosions also rocked the eastern Ukrainian city of Kharkiv early Saturday, sending plumes of smoke into the sky and triggering secondary explosions. Ukrainian officials accused Russia of using surface-to-air missiles in two largely residential neighborhoods.

Kharkiv resident Tetiana Samoilenko's apartment caught fire in the attack. She was in the kitchen when the blast struck, sending glass flying.

"Now I have no roof over my head. Now I don't know what to do next," the 80-year-old said.

From The Associated Press