Ukraine crisis: President Poroshenko in talks over rebel polls
Ukraine's president is to chair a crisis meeting of his security chiefs, following elections in rebel-held areas which Kiev describes as a "farce," the BBC reported.
In a TV address, Petro Poroshenko said Sunday's polls in parts of the eastern Donetsk and Luhansk regions could derail the "entire peace process."
Two pro-Russian leaders were declared the winners of the polls and are expected to be sworn on Tuesday.
The West says the elections were illegal, but Russia is backing them.
More than 4,000 people have been killed in fighting in eastern Ukraine since April.
Ukraine accuses Russia of arming the rebels and sending Russian regular troops across the border - a claim denied by Moscow.
A nominal ceasefire has been in place in eastern Ukraine since 5 September, but there have been repeated violations by both sides.