Kiev (AFP) - Ukrainian President Petro Poroshenko threatened to tear up a peace plan with pro-Russian separatist rebels on Monday after they defied Kiev and held elections intended to demonstrate their independence.
"These pseudo-elections are a gross violation" of a September truce deal, he said in an address to the nation.
Poroshenko said he and security chiefs would "re-examine" Kiev's commitments to the ceasefire deal on Tuesday, including "abolition" of a key element that offered separatists autonomy within Ukraine's existing borders.
The elections on Sunday were meant to provide legitimacy to the rebel administrations that have taken control of two regions in Ukraine's industrial east since war broke out in April.
Russia, which denies Western accusations that its troops are actually taking part in the fighting, recognised the elections. The United States condemned the vote as a sham and along with European powers, blasted Moscow's support for what they said were illegitimate polls.
"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 endorsement 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 military alliance concern.
- Russian defiance, sanctions -
Russia risks an intensifying of tough EU and US economic sanctions, but ignored Western appeals not to recognise the rebel vote, saying 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."
- New fighting -
The fear in Ukraine is that the vote will prove the death knell of the already battered September ceasefire.
AFP journalists in the rebel stronghold of Donetsk reported heavy shelling between government and rebel forces after a day's lull around the ruins of the city's disputed international airport.
Fuelling fears that rebels could be readying a fresh offensive, Kiev repeated claims that it was seeing "intensive" movements of troops and weapons across the frontier on Monday.
International observers from the Organisation for Security and Cooperation in Europe -- which has been tasked with monitoring the ceasefire -- said an unmanned drone used as part of their mission was shot at from rebel territory on Sunday, but not hit.
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 insurgent brigades and the long columns of military trucks frequently seen in the area of the Ukraine-Russia border.
- Rebel leaders confirmed -
Under the September truce, whose signatories included Russia, both sides were meant to halt hostilities and start a process towards granting increased autonomy to the pro-Russian areas.
Emboldened by the staging of their vote, rebel leaders blamed Kiev for the continuing violence.
"Ukraine does not want peace, as it claims. Obviously it is playing a double game," the newly elected president of the self-proclaimed Donetsk People's Republic, Alexander Zakharchenko, told journalists.
Zakharchenko, already the undisputed commander in the city of Donetsk, took 75 percent of the roughly one million votes cast, according to final results released by rebel election officials.
The 38-year-old former electrician is set to be officially inaugurated as the rebel republic's leader on Tuesday.
In neighbouring Lugansk region, current insurgent supremo Igor Plotnitsky, a former Soviet army officer, won with 63 percent, the rebels said.