Donetsk (Ukraine) (AFP) - Shelling in the centre of the main rebel-held city in Ukraine's east killed a Swiss Red Cross worker Thursday, tearing badly at a weakly observed four-week truce meant to defuse Europe's worst crisis in decades.

The attacks in Donetsk were the first to strike the heart of the city since the signing of the truce on September 5 between Kiev and Moscow.

Parts of the eastern coal mining hub -- once home to nearly a million Russian speakers but now half-abandoned -- were on fire after rockets slammed into a 14-storey central shopping centre shortly before 6:00 pm (1500 GMT).

AFP reporters saw another shell shatter the windows of the Donetsk headquarters of the International Committee of the Red Cross (ICRC) and the body of the Swiss man lying face down nearby.

A Donetsk emergencies worker told AFP that the victim was an ICRC employee normally based in Geneva.

The ICRC confirmed the death in a tweet from its official account, saying: "One of our colleagues in Donetsk, Ukraine was killed when a shell hit close to our office. We're deeply distressed by this loss."

It was not immediately clear who was responsible for the attack.

But it represented a dangerous new escalation in a conflict that -- despite intensified European mediation -- has entered its sixth month with the death toll climbing above 3,200 and East-West relations plumbing a post-Cold War low.

Russia, which is accused by the West of militarily backing the pro-Moscow rebels holding Donetsk and other parts of eastern Ukraine, reacted to the ICRC worker's death.

"ICRC please accept our sincere condolences. He came to help and to save -- not to die," Russia's foreign ministry said in an English-language tweet.

It added the "bloodshed must stop" in eastern Ukraine.

NATO claims hundreds of elite Russian forces are forming the backbone of the insurgency in Ukraine.

The rebels recently surged back powerfully against a Ukrainian military campaign against them, before the ceasefire was worked out to create a buffer zone along the frontline. The truce, however, has been only patchily observed, and fighting in some areas has continued.

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Nearly 70 Ukrainian troops and civilians, along with an undisclosed number of separatist gunmen, have been killed since the start of the 12-point peace pact.

On Thursday, smoke billowed over the northern half of Donetsk as the rebels tried to stage a final push on the city's devastated airport, their strategic target since May.

"There is a huge fire burning at the airport. It is probably due to the fuel," a representative at the Donetsk separatist headquarters said as periodic rounds of machinegun fire echoed through deserted streets.

The rebel representative said gunmen had briefly entered a section of the main terminal of what was once the east's busiest air hub before they were repelled.

The rebels continue to reject Ukrainian President Petro Poroshenko's efforts to save the ex-Soviet country from disintegration through the offer of autonomy to its ethnically Russian parts.

The upsurge in violence prompted German Chancellor Angela Merkel -- viewed as Kiev's closest and most powerful European ally -- to call Russian President Vladimir Putin and remind him of Moscow's "responsiblity" to rein in the rebels.





- Russian gas war -





Ukraine's security concerns have been exacerbated by a new gas war with Russia that threatens to leave parts of the near-bankrupt country without heating through the long winter months.

Russia nearly doubled Ukraine's gas price a few weeks after the February ouster in Kiev of a Kremlin-backed president who had earlier rejected a historic EU trade and political association deal.

Kiev refused to make the extra payment and Russia's decision in June to cut Ukrainian shipments has fuelled an economic meltdown that has forced world powers to cobble together $27 billion (21 billion euros) in emergency aid.

The World Bank downgraded Ukraine's 2014 economic growth forecast to an eight-percent contraction -- three percentage points lower than its previous outlook and more in line with the view taken by other institutions.

"There is no easy way out of the current crisis," regional World Bank director Qimiao Fan warned.

Ukrainian energy chiefs meanwhile travelled to Brussels ahead of what both Kiev and Moscow said would be a new round of EU-brokered talks about the energy dispute.

But talks expected to take place on Friday were postponed. A European source told AFP that now "there will not be a trilateral meeting until at least the end of the weekend."

European officials did not immediately explain the apparent last-minute delays, but they came a day after EU member Slovakia reported a 50-percent drop in its Russian gas supplies.