Fears of all-out Ukraine war grow

New columns of tanks, trucks and heavy artillery have rumbled towards the pro-Moscow rebel stronghold of Donetsk as fears grow of a return to all-out fighting in war-torn eastern Ukraine.

The Netherlands meanwhile held an emotional ceremony for the 298 victims of Malaysia Airlines flight MH17, which was shot down in July, focusing the world's eyes on the conflict in the ex-Soviet state.

Pro-Russian separatist authorities in Donetsk said that the delayed removal of MH17 plane debris would begin on Tuesday despite the fighting, but Dutch investigators say that no date has officially been fixed and that the situation is being assessed daily.

About 1600 relatives and friends of the dead from 18 countries gathered alongside members of the Dutch royal family in Amsterdam for Monday's ceremony.

Among the mourners were Dutch schoolchildren who laid flowers for classmates killed as they set out for their summer holidays on board the doomed flight from Amsterdam to Kuala Lumpur.

"What if the holiday had started a day later? What if the plane had been late? What if I wake up and realise it was all just a dream?" Prime Minister Mark Rutte said in his address.

"But there is no what if. Only the harsh reality of 298 dead."

Ukraine and the West blame Russia for supplying the pro-Kremlin separatists with the missile that shot down the plane, while Moscow and the rebels have pointed the finger at Kiev's forces.

The human toll of the conflict rose again on Monday when three civilians and one Ukrainian soldier died as rebel shelling hit a residential area near a Ukrainian checkpoint in the frontline town of Avdiivka, some 10 kilometres north of Donetsk.

Seven people were injured, according to the Donetsk region administration, which is loyal to Kiev and announced the incident.

Intense weekend shelling around Donetsk and more armoured columns heading to the city have fuelled concerns the rebels could be gearing up for an offensive after weeks of localised skirmishes.

An AFP journalist saw 28 trucks, six tanks and 14 howitzer artillery systems and two armoured personnel carriers driving through rebel territory around Donetsk on Monday.

AFP journalists also reported sporadic shelling in Donetsk overnight, some 24 hours after heavy bombardments rocked the rebel bastion in some of the fiercest fighting there since the September 5 truce deal.

At the MH17 ceremony in Amsterdam, 298 large candles burned in memory of the victims, 193 of whom were Dutch citizens, as flags flew at half-mast around the country.

Russian President Vladimir Putin said shelling at the rebel-controlled location by Ukrainian forces was preventing a probe, during a meeting with Malaysian Prime Minister Najib Razak on the sidelines of Monday's Asia-Pacific Economic Cooperation summit in Beijing.