A US soldier, right, instructs Ukrainian soldiers during joint training exercises on the military base in the Lviv region, western Ukraine yesterday.

Ukraine's president has warned his army to be ready to repel a "full-scale" Russian invasion, as fears mount of a return to all-out warfare in eastern Ukraine.

Ukrainian government forces and Russian-backed separatists fought a fierce battle on the outskirts of the separatist stronghold of Donetsk this week in the most serious bout of fighting since a haphazardly observed ceasefire came into force in February.

"The military must be ready as much for a renewal of an offensive by the enemy in the Donbass as they are for a full-scale invasion along the whole length of the border with Russia. We must be truly ready for this," Petro Poroshenko said in an address to the Ukrainian parliament yesterday. "We must be really prepared for this."

Mr Poroshenko claimed there are already 9,000 Russian troops in separatist-held territory inside Ukraine, and said there was a "colossal threat" that Russian-backed forces would launch large-scale operations in the near future. Russia denies deploying troops to east Ukraine.

Ukrainian generals said they would order heavy weapons back to the frontline to respond to what they described as a large-scale separatist offensive.

The withdrawal of high-calibre artillery and armour was a key part of the Minsk peace accords, and the move has raised fears that the ceasefire is close to total collapse.

Russian officials last night blamed Ukraine for the violence, accusing Kiev of deliberately jeopardising a shaky ceasefire that has slowed but not stopped the war since February.

"The Ukrainian side has taken steps to aggravate tensions many times in the past in the run-up to some major international events. This used to happen and we are seriously concerned now over the most recent manifestation of such activity," Dmitry Peskov, Vladimir Putin's spokesman, said yesterday.

Mr Peskov appeared to be referring to continued peace talks and an upcoming G7 meeting, to which Mr Putin is not invited.

Earlier, Sergey Lavrov, the Russian foreign minister, said the February Minsk ceasefire agreements were "constantly under threat because of the actions of the Kiev authorities, trying to walk away from their obligations to foster direct dialogue with Donbass."

Mr Lavrov's comments appear to be a response to earlier calls from the United States for Russia to use its influence with the separatists to halt the fighting.

Ukraine said up to 1,000 rebel fighters backed by up to a dozen tanks and heavy artillery launched an assault on their positions in Marinka, a western suburb of Donetsk, in the early hours of Wednesday morning.

Alexander Basurin, a military spokesman for the Donetsk People's Republic, claimed the separatists had counter attacked in response to a Ukrainian assault.

Dozens died in the fighting, according to reports by either side, with the separatists reporting 14 military and five civilian casualties.

The Ukrainians said five of their soldiers were killed on all fronts, four of them at Marinka.

Observers from the OSCE special monitoring mission inside separatist-held Donetsk said they saw a number of armoured vehicles heading towards the line of contact on Tuesday night and heard outgoing artillery and rocket fire from 04:30 in the morning.

The heavy fighting on the outskirts of Donetsk on Wednesday was the most severe in months. The ceasefire called in February has been violated almost daily, but hostilities had tapered off after the agreement.

Yesterday, rebels shelled the town of Avdiyivka just north of Donetsk, according to a Facebook post from Vyacheslav Abroskin, the police chief for the government-controlled sector of the Donetsk region. He said an unspecified number of civilians were wounded.

The intensity of the combat the day before raised fears of full-scale fighting resuming in the war that has already killed more than 6,400 people since April 2014.

Meanwhile, US President Barack Obama will urge European Union leaders to maintain sanctions against Russia over its aggression in Ukraine at the upcoming G7 meeting, where he will also hold a bilateral meeting with Iraqi Prime Minister Haider al-Abadi, US officials said.

Mr Obama will arrive in Germany on Sunday for the summit of leaders from the world's top industrial nations. (© Daily Telegraph, London)

Irish Independent