Ukrainian President Petro Poroshenko was to meet security chiefs Tuesday 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 on Sunday were backed by Russia but condemned by Ukraine, the United States and EU powers.
Poroshenko, speaking late Monday, said "these pseudo elections are a gross violation" of the truce deal signed in Minsk on September 5 truce deal.
The accord was meant to pave the way for an end to the seven month separatist conflict with a ceasefire and an offer of autonomy, though not independence, for the pro-Russian insurgents.
Constant ceasefire violations have already undermined the truce, with fighting breaking out again Tuesday near the rebel-held city of Donetsk. More than 4,000 people have died in the war, which has sparked the biggest diplomatic crisis between Russia and the West since the Cold War.
Poroshenko said his National Security and Defence Council was to consider "abolition" of the law offering autonomy -- the heart of the overall peace plan.
"The pseudo-election torpedoed the law and sharply aggravated the situation," Poroshenko said, vowing only to deal with "legitimately elected local self-government bodies, but not... bandits who crown themselves."
The defence chiefs meeting was scheduled for 5:00 pm (1500 GMT), the presidency told AFP.
The inaugurations of the winners of the two controversial elections in the Donetsk and Lugansk regions were due to take place just a few hours ahead of Poroshenko's meeting in Kiev.
Separatist leaders were quoted late Monday by Russian news agency Interfax as saying that they were ready for "dialogue," but only on an equal basis with Kiev. They said any laws passed in Kiev without their consent would have no force.
Meanwhile, artillery bombardments started up again outside Donetsk, an AFP correspondent reported.
"Very heavy firing started from 6:30 this morning," said local resident Tatyana. "It's hellish."
Ivan, another Donetsk resident, said he feared Poroshenko's statement signalled the end of the ceasefire. "It's clear that the fighting will start up again," he said.
The United States followed Europe in hammering Sunday's rebel polls, which showed Ukraine's inability to control the eastern region, and were conducted without recognised election observers. Only Moscow endorsed the elections, a move likely to harden Western resolve to maintain punishing economic sanctions against Russia.
"These sham elections contravened Ukraine's constitution... and the most basic electoral norms," said the White House, while the State Department warned Moscow that recognising the polls "would only serve to isolate it further".
German chancellor Angela Merkel's top spokesman described as "incomprehensible" Moscow's approval of the vote -- in which the Kremlin-backed candidates faced no serious competition -- and warned this would "further aggravate the crisis."
NATO's supreme allied commander, US General Philip Breedlove, warned of a "revanchist Russia" whose recent ramping up of military flights into European airspace was causing the Western alliance concern.
Russian defiance, sanctions
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.
Its deputy foreign minister piled further pressure on Kiev by demanding it call a definitive end to military operations in the east and talk to the rebels on equal terms.
"This work can bring results only on condition of equal dialogue based on mutual respect, with Kiev renouncing military operations and the notorious 'anti-terror operation'," Grigory Karasin told state news agency TASS.
In New York, Russia also blocked an attempt in the UN Security Council to criticise the elections.
French President Francois Hollande said sanctions against Russia are "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."
The new EU foreign policy chief, Federica Mogherini, told The Guardian newspaper on Tuesday that it would be "extremely difficult, if not impossible" to come up with a new peace initiative if September's Minsk accord collapses.
The separatist uprisings in the pro-Russian corner of Ukraine started shortly after Russia's troops invaded and annexed Crimea, a southern Ukrainian region, in March.
Moscow justified that dramatic redrawing of the map by saying it needed to protect ethnic Russians from a surge of Ukrainian nationalism following a pro-Western revolution in the capital Kiev a month earlier.
It claims to provide only diplomatic and humanitarian aid to the eastern rebels, despite the heavy firepower boasted by some of the insurgents and the long columns of military trucks frequently seen in the area of the Ukraine-Russia border.
Former electrician turned insurgent leader Alexander Zakharchenko won Sunday's election to head the self-declared Donetsk People's Republic. In neighbouring Lugansk region, current insurgent supremo Igor Plotnitsky, a former Soviet army officer, was the winner.