Ukrainian President Petro Poroshenko is due to meet security chiefs to "re-examine" an already teetering peace accord with pro-Russian separatists after they defiantly staged elections banned by Kiev.
The elections of leaders in two unrecognised statelets in eastern Ukraine were backed by Russia but condemned by Ukraine, the United States and EU powers.
Poroshenko, speaking late on Monday, said "these pseudo elections are a gross violation" of the September 5 truce deal.
That accord was meant to pave the way for an end to the seven-month separatist conflict with a ceasefire and an offer of autonomy, but not independence, for the pro-Russian separatists. Fighting, including frequent violations of the ceasefire, has already cost more than 4,000 lives and sparked the biggest crisis between Russia and the West since the Cold War.
A Tuesday meeting of the National Security and Defence Council would consider "abolition" of the key law offering autonomy, Poroshenko said.
"The pseudo-election torpedoed the law and sharply aggravated the situation," he said, vowing only to deal with "legitimately elected local self-government bodies, but not ... bandits who crown themselves."
The winners of the two controversial elections in the Donetsk and Luhansk regions were expected to be inaugurated on Tuesday.
Ready for 'dialogue'
The separatist figures were quoted late on Monday by Russian news agency Interfax as saying that they were ready for "dialogue", but only on an equal basis with the government in Kiev. They said any laws passed in Kiev without their consent would have no force.
While the White House described the elections as "sham", the State Department warned Moscow that recognising the polls "would only serve to isolate it further".
Russia risks an intensifying of tough EU and US economic sanctions after declaring it "respected" the outcome of the poll.
"Those elected have received a mandate to resolve the practical issues of re-establishing normal life in the region," Moscow's foreign ministry said in a statement.
In New York, Russia also blocked an attempt in the UN Security Council to criticise the elections.
France's President Francois Hollande said sanctions against Russia were "essential ... but they should not be the sole response.
"The objective is to convince Moscow and the separatists to renounce escalation and to return to a dialogue."
Former electrician turned insurgent leader Alexander Zakharchenko won Sunday's election to head the self-declared Donetsk People's Republic. In neighbouring Luhansk region, former Soviet army officer Igor Plotnitsky was the winner.