Donetsk (Ukraine) (AFP) - Heavy artillery fire on Wednesday rocked east Ukraine's pro-Russian rebel bastion of Donetsk, after international monitors warned over escalating violence following the arrival of columns of insurgent reinforcements.
The explosions of mortars being fired from near the centre towards government positions at the ruined airport rumbled on from early in the morning, setting off car alarms, an AFP correspondent said.
Donetsk's city hall said in a statement "the sound of artillery fire and explosions can be heard in all districts" of the mining hub.
Ukraine's military said Wednesday one soldier had been killed and two wounded, including one at the airport, as its positions came under repeated shelling around the region.
The intensified shelling, the heaviest since the weekend, comes after observers from the Organization for Security and Cooperation in Europe (OSCE) in east Ukraine warned that growing clashes could tip the region back into all-out conflict despite a ceasefire deal.
- Unmarked convoys -
A frequently-violated truce has been in place in the east of the former Soviet republic since September. It has halted clashes along much of the frontline but not stopped bombardments at strategic flashpoints.
Government forces also accused the rebels of trying to capture a strategic location along the volatile frontline, delineated as part of the ceasefire deal, north of the second-largest rebel stronghold Lugansk.
The Lugansk region governor, who is loyal to Kiev, said there were increased artillery bombardments along the frontline close to the city.
A spokesman for the OSCE, which is monitoring the ceasefire, cautioned Tuesday that there was a "rising" risk of an escalation in the conflict, which has claimed more than 4,000 lives in total since April, according to UN figures.
Earlier Tuesday, OSCE observers reported seeing a convoy of 43 unmarked military trucks -- five towing Howitzer heavy artillery pieces and another five towing multi-launch rocket systems -- travelling into the rebel stronghold of Donetsk.
It was the latest in a string of recent sightings of unmarked trucks and heavy weapons heading towards the frontline in rebel-controlled areas.
Ukraine and Western countries believe they are Russian military material.
Russia has consistently denied that it is involved in the fighting in east Ukraine.
But it openly gives political backing to the self-declared separatist statelets and it is unclear how else the rebels could have acquired the heavy weaponry typical of a regular army.
Russia deployed unmarked troops to seize the Ukrainian peninsula of Crimea in March, denying at the time that they were its forces before admitting they had sent in soldiers.
- Putin faces Western leaders -
Ukraine's envoy to the United Nations, Yuriy Sergeyev, wrote on Twitter Tuesday that Kiev is now convinced Moscow is planning a "full-scale invasion into Ukraine."
The crisis over Ukraine has sent relations between Russia and the West plummeting to their lowest point since the Cold War.
Russian President Vladimir Putin is facing renewed Western diplomatic pressure over the issue during a week of high-level international talks.
Putin discussed Ukraine with US President Barack Obama and Australian Prime Minister Tony Abbott at a trade summit in Beijing.
Earlier Tuesday, US deputy national security adviser Ben Rhodes told reporters: "We continue to be deeply troubled by Russian activities. If they continue... it's a recipe for isolation."
Australia will host this week's G20 summit in Brisbane which Putin is also to attend amid public anger over allegations Russia supplied rebels with the missile that shot down Malaysia Airlines flight MH17 in July, killing all 298 people onboard including 38 Australian citizens and residents.
The United States and European Union have shown their anger towards Russia over Ukraine with a string of sanctions designed to weaken its economy. The ruble has lost some 25 percent of its value this year.
EU foreign ministers are set to hold a meeting on Ukraine next Monday and will discuss the option of more sanctions, EU foreign policy chief Federica Mogherini said in Berlin.
But German Chancellor Angela Merkel said that while EU member states were considering adding pro-Russian separatists to existing sanction lists imposed on Moscow, no more economic sanctions were planned "at the moment".
In a sign of how high suspicions are running, Russia refused to endorse a UN resolution on Bosnia that Moscow said would push the Balkan country towards NATO and the European Union -- a scenario that led to the conflict in Ukraine.