Ukrainian tanks and fighter bombers on Tuesday launched a ferocious assault against pro-Russian separatist insurgents after rejecting European attempts to save a tenuous 10-day truce.
Western-backed President Petro Poroshenko told the nation in an emotional late-night address that his peace plan for Ukraine's worst crisis since independence was being used by the militias to regroup and stock up on heavy arms from Russia.
"After examining the situation I have decided, as commander-in-chief of the armed forces, not to extend the unilateral ceasefire," the 48-year-old said from his office.
"The separatists' leaders have demonstrated their unwillingness and inability to control the actions of the terrorist units and marauding gangs under their control."
Ukrainian defence ministry spokesman Oleksiy Dmytrashkivsky said a "massive artillery and air offensive" had been unleashed in the eastern rustbelt -- home to seven million mostly Russian speakers.
Russia immediately expressed its "deep regret" over Poroshenko's decision while France's foreign minister promised that there would be no letup to Western efforts to bring a lasting peace to Ukraine.
Both separatist fighters and pro-Kiev leaders reported heavy exchanges of artillery fire and air bombardments across the economically-vital Russian border regions of Lugansk and Donetsk.
The regional administration of Donetsk -- which along with Lugansk has declared its allegiance to Moscow -- said four civilians were killed and five wounded when their bus came under fire near the town of Kramatorsk.
Both rebels and Kiev confirmed a heavy tank battle being waged in near the Donetsk region town of Karlivka and intense clashes in the nearby village of Mariinka.
The Donetsk administration said the region's roads had become too dangerous for travel and suspended several intercity bus routes.
The unpredictable spells of fighting have also claimed the lives of an Italian photographer and several reporters from both Russia and Ukraine. Western-backed Hromadske TV in Kiev on Tuesday reported the abduction of one of its journalists and a cameraman in the Lugansk region.
Poroshenko's decision came just hours after the leaders of France and Germany joined him on a conference call to Russian President Vladimir Putin -- the third such conversation in five days.
French President Francois Hollande and German Chancellor Angela Merkel were in rare agreement with Putin that Poroshenko should extend the truce to give indirect talks between separatist commanders and Kiev a chance.
But the contacts have mostly failed to halt 11 weeks of fighting that have killed more than 450 people and shuttered dozens of coal mines and steel mills whose operation is vital to Ukraine's teetering economy.
Poroshenko told the three leaders that insurgents had attacked Ukrainian positions more that 100 times during the truce.
The separatists likewise accuse government forces of having continued to shell the dozen cities and towns under their control during the official halt of hostilities.
"Calls for the militias to lay down their arms can be discussed only after the withdrawal of Ukrainian forces," the Lugansk region's self-declared premier Vasyl Nikitin told Russia's Interfax news agency.
Poroshenko had come under extreme pressure from Ukrainian nationalists to relaunch the offensive and meet his May 25 election promise to reunite Ukraine.
Hundreds rallied outside his office in Kiev on Sunday demanding an end to the truce. Campaign rivals such as former premier Yulia Tymoshenko have also spoken out strongly in favour of a more forceful military response.
But Poroshenko insisted in his address to the nation that he was not abandoning his earlier peace plan altogether.
"We are even ready to return to a ceasefire at any moment," he said.
"Peace has been and will remain my main goal. Only the means to achieve it have changed."
Both Kiev and its Western allies have accused Putin of helping to arm and fund the separatists in reprisal for the February ouster of a Kremlin-backed leader who had rejected closer European ties.
The Kremlin denies all charges but still faces the threat of devastating economic sanctions should Putin fail to demonstrate a clear desire to resolve the conflict.
The Russian strongman has publically taken a more conciliatory approach to Kiev in response.
He has pressed for direct negotiations and a long-term truce. Western powers have also reported a significant withdrawal of Russian troops from the border with Ukraine.
But Putin has notably refused to meet the main Western demand of calling on the rebels to lay down their weapons and relinquish control of roadblocks and border crossing across Lugansk and Donetsk.
Poroshenko for his part has refused to meet directly with separatist leaders who have "blood on their hands".