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", reports GHN based on BBC.
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.
The clashes in the east began a month after Russia annexed Ukraine's southern Crimea peninsula.
Addressing the nation on Monday, President Poroshenko said the 2 November elections in Donetsk and Luhansk were "a farce at gunpoint", which had nothing to do with the expression of the voters' will.
He stressed that Ukraine would never recognise the vote in the two self-proclaimed rebel republics.
Mr Poroshenko said the polls were "a gross violation" of September's Minsk agreement - a roadmap to a peaceful settlement agreed by Ukraine, Russia, the Organization for Security and Co-operation in Europe (OSCE) and also rebel delegations.
He added that he would hold a meeting of Ukraine's Security and Defence Council on Tuesday to propose abolishing a law granting special self-government to rebel-held areas, something which had been approved by Kiev as part of the peace process.
Ukraine and the West had always insisted that the rebel territories must abide by the Minsk deal and hold local elections under Ukrainian law in December.
Late on Monday, the US said it "condemns the illegitimate, so-called 'elections' held on Sunday by Russia-backed separatists in parts of Donetsk and Lugansk".
In a statement, White House National Security Council spokeswoman Bernadette Meehan added that Washington was "concerned by a Russian Foreign Ministry statement that seeks to legitimise these sham 'elections'".
