Gunmen from the newly proclaimed People's Republic of Donetsk have taken another step towards snapping their region off from the rest of Ukraine, seizing control of a key Central Election Commission office and declaring that the country's May 25 parliamentary and presidential vote will not be held here.

The election now looms as the next flashpoint in Ukraine's worsening political crisis. Separatists in the oblasts, or provinces, of Donetsk and Lugansk have vowed the votes won't be held in either region, which together account for almost 15 per cent of Ukraine's pre-crisis population of 46 million.

However, Ukraine's interim government says the vote – seen as key to keeping the country from further fracture – must go ahead under any circumstances. It's the first election since the Moscow-backed government of Viktor Yanukovych was ousted in February by pro-Western protesters, a revolt that many Russian-speaking Ukrainians believe has left the country without a legitimate government.

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Nine pro-Russian fighters, carrying AK-47 assault rifles and Makarov pistols, burst into a local government building Wednesday in the city of Donetsk that was to serve as a nerve centre on election day. A witness told The Globe and Mail that the gunmen instructed staff to leave the premises and that the election was illegal since Mr. Yanukovych – whose five-year term was due to expire in 2015 – was still president.

Mr. Yanukovych is a Donetsk region native who narrowly won a 2010 election, taking more than 90 per cent of the vote in Donetsk and Lugansk. Even in Donetsk, that popular support evaporated when Mr. Yanukovych's extravagant lifestyle was exposed in the wake of the revolution in Kiev and his escape into exile in Russia.

The camouflage-clad gunmen arrived at the District Election Commission No. 42, on Artyoma Street in downtown Donetsk, at the same time as a team of foreign observers was visiting to check on preparations for the May 25 vote.

"I tried to walk past them and they blocked me and said 'you can't come this way,' " said one foreign observer, who spoke on condition of anonymity, since he was not authorized to speak to media. "They showed a piece of paper from the Donetsk People's Republic which said that the [Election Commission] was now closed and that since there already is a president of the country, there's no need to have the elections to be held, and to go home and leave all our things."

The same building on Artyoma Street, which oversees the operation of 88 polling stations covering some 150,000 voters, was used by the separatists during a Sunday referendum that saw the rebels claim 89-per-cent support for the establishment of a sovereign Donetsk. The Central Election Commission did not help prepare or oversee that vote, which Interim Ukrainian President Oleksandr Turchynov slammed as a "criminal farce."

Wednesday's building takeover left the separatists in possession of the Election Commission's computers, which contained personal information, including voter details and the names and addresses of members of political parties that support Ukrainian unity.

"All the information on the computers is now owned by the DPR," said the foreign observer.

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He said members of the pro-European parties had already been receiving threatening e-mails before the computers and their data were seized.

The closure of the election office in Donetsk came as the Ukrainian government hosted roundtable talks in Kiev aimed at calming the crisis by discussing a potential devolution of powers to the country's restive regions. However, the possibility of a breakthrough seemed slim since the leaders of the Donetsk and Lugansk rebels were not invited to join the negotiations.

Mr. Turchynov's government has alleged that the fighters and politicians of the Donetsk People's Republic get orders and money from neighbouring Russia. Moscow annexed the southern region of Crimea following a controversial March referendum there.

"Those with weapons in hand who are waging a war against their own country and dictating the will of a neighbouring country will answer before the law. We will not yield to blackmail," Mr. Turchynov said. "We are ready to listen to the people of the east but they must not shoot, loot or occupy government buildings."

Many believe eastern Ukraine is now sliding towards civil war, if it isn't already embroiled in one. On Tuesday, seven Ukrainian soldiers were killed when their armoured column was ambushed near Kramatorsk, a city north of Donetsk. It was the biggest loss of life suffered by the Ukrainian army since the pro-Russian uprising began last month.

In an interview with Bloomberg television, Russian Foreign Minister Sergei Lavrov said he didn't see how the May 25 election could be held under the current circumstances.

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"In east and south of Ukraine there is a war, a real war," he said. "And if this is conducive to free and fair elections then I don't recognize what free and fair is."