New unidentified armoured columns rumbled toward the pro-Moscow rebel stronghold in eastern Ukraine on Monday as fears grew of a return to all-out fighting in the war-torn region.

The Netherlands meanwhile was set to hold an emotional ceremony for the victims of the MH17 flight shot down over the separatist-held eastern Ukraine in July in a tragedy that brought the conflict in the ex-Soviet state to the international fore.

Flags flew at half mast in the country and at Dutch diplomatic missions abroad ahead of a commemoration in Amsterdam for the 298 people killed when the Malaysia Airlines flight was blown out of the sky.

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 forces.

On the ground in Ukraine, intensified weekend shelling around the rebel stronghold of Donetsk and more armoured columns heading to the city ratcheted up concerns the rebels could be gearing up for an offensive after weeks of isolated skirmishes

An AFP journalist saw a total of 21 trucks, six tanks and 14 howitzer cannons driving through rebel-territory to Donetsk on Monday, after similar hardware arrived on Sunday and after the West sounded a warning over heavy military reinforcements for the Kremlin-backed separatists.

The White House expressed grave concern at reports of Russian military reinforcements in eastern Ukraine, warning that any separatist efforts to seize more territory would be a “blatant violation” of a September ceasefire agreement that had halted full-scale fighting but failed to stop shelling at key flashpoints.

“We are very concerned by intensified fighting in eastern Ukraine, as well as numerous reports... that Russian backed and supplied separatists are moving large convoys of heavy weapons and tanks to the front lines of the conflict,” US National Security Council spokeswoman Bernadette Meehan said in a statement.

And the European Union’s foreign policy chief, Federica Mogherini, said reports of military reinforcements were a “very worrying development” and called on Russia to prevent further movement of “troops, weapons and equipment”.

The MH17 memorial in Amsterdam is to be attended by 1,600 relatives of those killed in the July 17 disaster, 193 of whom were Dutch citizens, along with the Dutch royal family and Prime Minister Mark Rutte.

The remains of 289 of the victims have so far been identified but Dutch officials have admitted that the remaining dead may never be recovered as the security situation around the crash site remains volatile.

The unidentified military columns spotted in the east in recent days by foreign journalists and the Organisation for Security and Cooperation in Europe (OSCE) have raised concerns, as Ukraine’s military on Sunday repeated allegations that Russia is covertly deploying troops to bolster rebels ahead of a fresh offensive.

Russia has repeatedly denied that it is involved in the fighting in the east.

However, it openly gives the rebels political and humanitarian backing and it is not clear how the insurgents could themselves have access to so much sophisticated and well-maintained weaponry.

The fresh troop movements have fuelled fears of a total breakdown in the two-month truce, with the war having already killed some 4,000 people since April, according to UN figures.

In March, Russian soldiers without identification markings took over the southern Ukrainian region of Crimea, with Moscow annexing the peninsula shortly after.

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

The conflict has sent relations between Western backers of Ukraine and Russia to their lowest levels since the end of the Cold War.

Russian President Vladimir Putin kicked off a fraught week of diplomacy that will take in the Asia-Pacific Economic Cooperation summit in Beijing and Group of 20 meeting in Brisbane, Australia, where he looks likely to face a hostile reception from Western leaders.

Russia’s economy is suffering from European Union and US sanctions imposed in response to Moscow’s support for the separatists, with the ruble losing some 25 per cent of its value this year.

But Putin sounded a confident note as he shrugged off concerns over the ruble’s collapse, putting it down to short-term speculative trading.

“I think it will stop soon given the actions taken by the central bank in response to speculators,” Putin said in a speech in Beijing

source : gulfnews