Two low-flying attack helicopters swept over the southern Russian city of Belgorod early Friday, firing rockets and blowing up fuel tanks, according to Russian media. Local governor Vyacheslav Gladkov immediately blamed Ukraine for the attack. The claim could not be verified. Video of the attack surfaced early Friday on Russian Telegram channels, while local media reported that eight fuel tanks were burning, with a risk that the fire could spread, and that at least 19 residents from adjacent areas were evacuated. Ukrainian Foreign Minister Dmytro Kuleba, when asked about the allegations of Ukrainian involvement, said he could not confirm or deny the claim because he did not have all the relevant military information. Ukraine has not previously attacked targets in Russian territory during the war. Russia’s military said on March 27 that it struck a fuel depot in the western Ukrainian city of Lviv in a rare strike on the city that’s become a refuge for diplomats and Ukrainians. Ukraine military spokesman Oleksandr Motuzyanyk said Friday that Ukraine did not bear responsibility for catastrophes and incidents in Russia. He declined to confirm or deny Ukrainian involvement, but said it was not the first time Russia had made such accusations. Ukraine’s operation was defensive, “to resist Russia’s military aggression in the territory of Ukraine,” Motuzyanyk added. After Russia invaded Feb. 24, Ukrainian forces initially mounted a defensive stance focused on Kyiv and other major cities, and in recent days have been retaking settlements near the capital and along the front lines. Ukrainian presidential adviser Oleksiy Arestovych seconded his colleagues that Ukraine was focused on defending itself. “Maybe someone smoked in the wrong place” and caused the fire, he said, adding: “Everything that happens on Russian territory is the responsibility of the Russian leadership. All questions to them.” Kremlin spokesman Dmitry Peskov said Friday that President Vladimir Putin has been informed about the incident. He said it was “certainly” an escalation, adding: “This is not something that can be perceived as creating conditions comfortable for the continuation of negotiations.” Peskov added that Russia’s control of its airspace was not in doubt. As for what happened, it “is up to our law enforcement agencies, not us, to make assessments,” he said. On Tuesday, a series of explosions also occurred at a Belgorod ammunition storage facility. Russian media initially said the explosions appeared to be caused by firing from the Ukrainian side, but officials later blamed the blasts on a fire on the premises. The latest incident risks undermining progress in talks between the two sides aimed at reaching a peace deal, now at a delicate stage, after Ukraine offered concessions to Russia on Tuesday in return for a military withdrawal. Russian negotiators announced Tuesday that Moscow’s forces would de-escalate their combat operations near Kyiv and Chernihiv to “build trust,” focusing their fight on eastern Ukraine. The announcement caused outrage among prominent hard-line state television presenters, pundits and on social media. But Ukrainian President Volodymyr Zelensky said he did not trust Russia’s announcement of a de-escalation, telling Ukrainians in one of his regular addresses Thursday: “We don’t believe anyone, not a single beautiful phrase.” U.S. officials have also been skeptical of Moscow’s announcement, seeing it as a sign that Russia is probably taking time to regroup and reorganize its attack.