This handout picture taken on January 13, 2015 by Anti-Terrorist Operation press service shows a damaged bus after it was hit by a long-range Grad rocket apparently fired by pro-Russian insurgents in Volnovakha
Tonenke (Ukraine) (AFP) - Pro-Kremlin insurgents unleashed a massive rocket assault in Ukraine Wednesday as Kiev and Moscow traded blame for a bus shelling that killed 12 in the war's bloodiest incident since a September truce.
The heavy calibre shells and grenades whistled through the sky every few minutes and dug huge craters in the snowy fields along a front line that skirts a devastated village 10 kilometres (six miles) northwest of the eastern rebel stronghold Donetsk.
Blasts inside Tonenke itself -- abandoned by all but a handful of its 300 residents -- flattened buildings and mangled paved roads that stetch toward a disputed airport on the edge of Donetsk.
"This is all-out war," a volunteer soldier who adopted the nom de guerre "The Pastor" told AFP on his way out of a Donetsk suburb used by Ukrainian troops to support a skeleton force holding on to the airport since May.
"The attacks start early in the morning and end deep into the night. There is a quiet spell of one or two hours at most. It has never been like this before.""
The type of long-distance exchanges piercing the skies around the militants' capital on Wednesday have caused hundreds of civilian casualties throughout the nine-month campaign.
A long-range Grad rocket killed 12 people on Tuesday when it exploded near a commuter bus travelling toward Donetsk from a government-controlled city on Ukraine's southeast coast.
Images of the yellow bus's shattered frame standing in a field of bloodied snow underscored how distant a truce remains after the death of more than 4,700 people and effective destruction of Ukraine's industrial base.
Ukrainian President Petro Poroshenko told the nation that Tuesday's rocket was fired by rebels, while responsibility rested on "those who stand behind them -- those whose hand feeds them and arms them, drills them and inspires them to commit bloody crimes."
The transparent reference to Moscow -- charges which President Vladimir Putin rejects -- was followed by Kiev claims that the fighters employed a massive 30-barrel flamethrower, a type used by Russia but not Ukraine.
Kiev said insurgents used it for the first time overnight to attack the eastern village of Vesele.
This type of system "only exists in the operational service of the Russian army. It is not operated by us," Ukrainian defence ministry spokeswoman Viktoria Kushnir told AFP.
- Russia 'outraged' -
Russia issued no immediate comment. But the foreign ministry's rights envoy called the bus incident "another crime of the Kiev military".
"We are outraged. This undermines all peace settlement efforts," Konstantin Dolgov told the TASS news agency.
Russian Foreign Minister Sergei Lavrov later softened those comments by conceding that "there are... several versions (of the incident). We need to examine them."
Tuesday's incident marked the biggest single loss of civilian life since the warring sides signed a September 5 ceasefire that only partially stemmed the fighting and did little to resolve the insurgents' independence claims.
The rocket strike also damaged Poroshenko's efforts to set up a peace summit where Putin could personally sign a truce under which the Kremlin assumes responsibility for disarming the militias and dispelling their independence claims.
German Chancellor Angela Merkel -- the West's main mediator in Europe's deadliest conflict since the Balkan wars of the 1990s -- argues that such a meeting would be premature with violence still raging.
Putin has argued that the revolt in western Ukraine was a natural response by ethnic Russians to their "persecution" by the more nationalist leaders who ousted a Moscow-backed administration in Kiev in February last year.
Kiev now also plans to apply for NATO membership -- a defensive shift that the Kremlin views as both confrontational and a global security threat.
A new NATO delegation arrived in Ukraine on Wednesday for a week-long visit focused on "military and technological cooperation".
The vague diplomatic term usually refers to arms deliveries. Kiev defence officials said the NATO delegation would visit Ukraine's main arms manufacturer and the Antonov aviation plant.