Did they, or didn't they attack an oil depot in the Russian city of Belgorod? The local Russian governor claims two Ukrainian helicopters fired rockets while flying at low altitude. If so, they flew 35 kilometers over Russia, to attack rather than just defend its own borders.

The attack or fire started early on April 1. Belgorod's governor Vyacheslav Gladkov confirmed the incident on the messaging app Telegram.

Gladkov also said two workers were injured in the fire, and that some areas in the city were evacuated. The Russian oil firm Rosneft, which owns the fuel depot, said in a separate statement that no one was hurt and gave no information on what caused the blaze.

Ukraine's Foreign Minister Dmytro Kuleba says he cannot confirm or deny Ukraine was involved. In fact, he's quoted as saying, "I am a civilian," and so couldn't comment on the military.

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Ukraine's defense ministry also declined to comment, while one news agency quoted spokesman Oleksandr Motuzyanyk saying: "Ukraine is currently conducting a defensive operation against Russian aggression on the territory of Ukraine, and this does not mean that Ukraine is responsible for every catastrophe on Russia's territory. I will not confirm or deny these allegations."

Gladkov seemed to have few doubts. "A fire at the oil depot occurred as a result of an airstrike from two helicopters of the Armed Forces of Ukraine, which entered the Russian territory at a low altitude," he wrote.

The Kremlin wasn't very vocal, but spokesman Dmitry Peskov said the alleged strikes don't create "comfortable conditions" for the latest peace talks. Video images of the alleged attack were posted online and showed what looked like several missiles being fired from low altitude, followed by an explosion. 

News agencies as yet haven't been able to verify the footage but Reuters did obtain CCTV footage that showed an explosion. The date and time stamped on the footage corresponded with the fire at the oil depot and Reuters did confirm the buildings in the video match buildings in the area of the oil depot.

Ukrainian helicopter pilots have plenty of experience of flying low and fast to avoid being detected by military radar and air defense systems. They've been perfecting this technique in the Donbas region in eastern Ukraine for the past eight years. If true, some highly skilled pilots would have had to have been used, to fly at night and avoid detection.

This type of alleged attack by itself would not dramatically alter the war, but it would boost Ukrainian morale. If confirmed, it would be the first known time Ukraine has flown into Russian airspace to attack, bringing the conflict home to Russia.

This is the second explosion in the Belgorod district, after an ammunition depot caught fire on Wednesday, causing a series of blasts. At the time, Gladkov said authorities were waiting for the Russian defense ministry to establish its cause.

In the south, the International Committee of the Red Cross (ICRC) says it has postponed an attempt to evacuate civilians from the besieged city of Mariupol. There have been reports of aid being looted, and more than 50 buses held up, while traveling to carry people away to safety.

"The ICRC team, which consists of three vehicles and nine personnel, did not reach Mariupol or facilitate the safe passage of civilians today. "They will try again on Saturday to facilitate the safe passage of civilians from Mariupol.