The Kremlin said a ceasefire announced by Ukrainian President Petro Poroshenko is an ultimatum to pro-Russian separatists rather than an offer of peace, Russia's Interfax news agency has reported.
"This is not an invitation to peace and negotiations, but an ultimatum to militias in the southeast of Ukraine to lay down their arms," the Kremlin was quoted as saying.
It also claimed that a Russian checkpoint on the Ukrainian border had come under fire and demanded "an explanation and an apology" from Kiev.
More top news
The first victim of the Manchester bombing has been named as Georgina Callander, a student from Lancashire.
A 23-year-old man has been arrested in connection with the attack at Manchester Arena last night.
Theresa May says police think they know identity of lone bomber as she contrasts "warped" terrorist with courageous emergency services.