Ukraine said it had evidence that a cyber attack against government websites on Friday was likely to have been carried out by Russia, amid fears that Moscow may be planning military action against the country after security talks with the US and Nato failed.

“At the moment we can say that all evidence points to Russia being behind the attack,” Ukraine’s digital transformation ministry said in a statement on Sunday. “Moscow continues to wage hybrid war and is actively growing its information and cyber space capabilities.” But Kyiv said the investigation was still ongoing and had yet to formally attribute the attack to Russia.

Stopping short of blaming Moscow on Sunday, Jake Sullivan, national security adviser to US president Joe Biden, said: “It would not surprise me one bit if it ends up being attributed to Russia.”