A Russian governor in the border region of Belgorod said that early on Friday April 1, two Ukrainian Mi-24 helicopters crossed the border at low altitude before firing rockets at an oil facility 25 miles from the border.

Ukraine’s foreign minister, Dmytro Kuleba, said he could not confirm or deny reports of Ukrainian involvement in the strike as he did not have military information, Reuters reported. The Ukrainian defence ministry has not responded for a request for comment.

A number of prominent Ukrainian commentators have claimed that the attack could be a “false flag” meant to justify a Russian mobilisation or scuttle negotiations.

On Friday, the Kremlin spokesperson Dmitri Peskov fuelled those rumours by saying the attack could hamper negotiations, although he stopped short of announcing any concrete response over the alleged attack.

“What has happened is certainly not something that can be perceived as creating conditions comfortable for the continuation of negotiations,” Peskov said.

Video posted to social media on Friday appeared to show a helicopter strike using air-to-ground missiles and then a major fire at a facility said to be in Belgorod, with flames reaching dozens of metres into the air.

Reports showed that the facility continued to burn until midday on Friday, with dozens of firefighters dispatched to battle the inferno.

Other videos showed the helicopters, which are used by both Ukraine and Russia, flying in the region.

“The fire at the oil depot occurred as a result of an airstrike from two helicopters of the armed forces of Ukraine, which entered the territory of Russia at low altitude,” said the governor, Vyacheslav Gladkov. “There are no victims.”