A fresh explosion was heard around 1 p.m. local time (1000 GMT) on Friday in the Russian city of Belgorod, where a local official said Ukrainian forces hit a fuel depot earlier in the day, Reuters has reported, citing a witness.

Regional governor Vyacheslav Gladkov said two Ukrainian military helicopters struck the depot in the early hours of Friday, marking the first accusation of a Ukrainian air strike on Russian soil since Moscow's "special military operation" began in late February.

In response, Ukrainian Foreign Minister Dmytro Kuleba on Friday said he could not confirm or deny the Russian accusation because he does not possess all military information.

(With input from Reuters)