KIEV - Pro-Russian insurgents launched a fresh assault Thursday on an airport held by isolated Ukrainian forces as a month-old truce came under renewed strain and calls grew for the Kremlin to help halt the bloody revolt.
Ukraine also dispatched its energy chiefs to Brussels in a bid to convince the European Union to back up Kiev at crunch talks with Russia on the latest energy war with its westward-leaning but effectively bankrupt neighbour.
Nearly 70 Ukrainian troops and civilians - along with an undisclosed number of separatist gunmen who control swathes of eastern Ukraine - have been killed since Moscow and Kiev signed a 12-point peace pact on September 5.
But the five-month uprising has barely slowed and the rebels continue to reject Ukrainian President Petro Poroshenko's efforts to save the ex-Soviet country from breaking up by offering autonomy to its ethnically Russian parts.
Ten civilians died Wednesday in the shelling of a school and bus station in the main separatist stronghold of Donetsk. Both sides traded blame for the attack.
On Thursday, the resurgent rebels -- backed up by what NATO claims are hundreds of Russian elite forces -- mounted waves of all-out attacks on the devastated airport on the northern outskirts of Donetsk that has been their target since May.
Ukrainian defence spokesman Vladyslav Seleznyov said the militiamen used tanks to shell besieged government forces who control the main terminal but none of the roads leading to what was once the east's busiest air hub.
"At the moment, the situation at the airport is tense," said Seleznyov. "They are staging their second assault of the morning."
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.
The Kremlin said Putin told Merkel he backed peace and "stressed the need to prevent further attacks by Ukrainian units on civilian buildings in southeast Ukraine."
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 put together $27 billion (21 billion euros) in emergency aid.
The World Bank downgraded Ukraine's 2014 economic growth forecast to an eight-per cent 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.
The Ukrainian energy chiefs' discussions with the Europeans ahead of trilateral talks in Berlin on Friday became even more crucial when EU member Slovakia reported a 50-per cent drop in Russian gas supplies.
Russia had warned last week that it may cut European deliveries because some countries were re-exporting gas to Ukraine in breach of their contracts with the state energy giant Gazprom.
Slovakia refused to bow to the pressure and continued providing Ukraine with the largest quantity of gas provided by any of its western neighbours.
Ukraine's pipelines transmit just 15 per cent of the Russian gas imported by Europe.
But EU powers such as Italy -- reliant on the Ukrainian link for all of its Russian supplies -- fear that Kiev may be forced to tap into those flows once winter sets in.
Last year, Russian energy giant Gazprom supplied Ukraine with 25.8 billion cubic metres of gas -- about half its needs -- at an average price of $413.50 per 1,000 cubic metres.
At initial talks in Berlin last Friday it promised to lower that rate to $385 for six months as long as Ukraine admitted to owing Gazprom $5.3 billion in outstanding debts.
This would secure 5.0 billion cubic metres of gas Ukraine -- the absolute minimum it needs to survive the winter.
But Ukraine has balked at the conditions. It disputes the amount owed to Gazprom and wants to see gas flows resume before it makes the first payment -- conditions that Russia rejects.