Kiev: Escalating clashes between pro-Kremlin separatists and Ukrainian forces on Sunday killed 12 civilians and forced the new Western-backed leader to cancel a pivotal meeting with Russian President Vladimir Putin at the World Cup in Brazil.
An explosive security crisis on the eastern edge of the European Union that has claimed more than 550 lives and enflamed East-West relations has since Friday threatened to spiral into an all-out civil war.
Militias that the West and Kiev allege are being armed by the Kremlin used a Grad multiple-rocket system late Friday to mow down 19 Ukrainian soldiers and wound nearly 100 near the Russian border.
Further attacks killed 18 more troops and 20 civilians -- 12 of them in what Kiev said were missile and other overnight rebel strikes staged across the eastern rustbelt -- in violence that appeared to shatter any hope of a truce.
Kiev-backed authorities said six people were killed and eight wounded in a suburb of the million-strong rebel stronghold of Donetsk.
Municipal workers in neighbouring Lugansk said six people had also died and seven were injured in various overnight incidents in that separatist bastion of 425,000.
And an AFP correspondent at the morgue in Maryinka saw the corpses of eight people killed in clashes waged outside that village just west of Donetsk on Saturday afternoon.
The civilian toll is one of the highest recorded over a two-day span in a three-month conflict that has threatened the very survival of the strategic ex-Soviet state sandwiched between the EU and Russia.
And the military losses have profoundly dampened rising hopes in Kiev that its recent string of battlefield successes had finally convinced the rebels to sue for peace.
Ukrainian President Petro Poroshenko has vowed to kill "hundreds" of gunmen for every lost soldier and ordered an air-tight military blockade of Lugansk and Donetsk -- both capitals of their own "People`s Republics" that want to join Russia.
European leaders responded by joining forces with Putin in a bid to convince Poroshenko to put the breaks on violence first sparked by the February ouster of a Kremlin-backed leader and fanned by Russia`s subsequent seizure of Crimea.
The immediate hopes of a truce rested on a meeting between Putin and Poroshenko -- only the second since the latter`s May 25 election -- that seemed in the cards on the sidelines of the World Cup final in Rio de Janeiro.
Putin was due in Rio as part of his Latin American swing and the Brazilian presidency said Poroshenko had also accepted an invitation on Friday.
But the Ukrainian leader`s office said early on Sunday that Poroshenko was forced to cancel his attendance "considering the situation currently happening in Ukraine".The separatists` use of Grad systems -- featured heavily in Russia`s devastating assault on the Chechen capital Grozny in the 1990s -- has underpinned the most recent charges of the Kremlin`s direct involvement in the insurgency.
Putin rejects accusations of orchestrating the uprising to retain partial control over eastern Ukraine and punish Kiev for its decision to strike an historic EU alliance instead of a new Kremlin pact.
But Poroshenko argues that no truce with the rebels is possibile until his troops manage to seal the Russian border and halt the continuing flow of gunmen and arms.
The frontier became the conflict`s new frontline after last weekend`s evacuation by the rebels of a host of towns and cities that they had held since early April in the coal mining region of Donetsk.
The militias have since concentrated their forces around Donetsk and Lugansk and are hoping for new weapons deliveries to revive their campaign.
A new source of tension between the Kremlin and Kiev emerged when Moscow said one person was killed and two injured when a shell fired from inside Ukraine hit a residential area near a small Russian border town.
The Russian foreign ministry said the incident could lead to "irreversible consequences," laying the blame on Kiev.
A top Ukrainian military spokesman said Ukrainian forces were responding to another Grad rocket attack launched from that border region overnight.