Snizhne (Ukraine) (AFP) - Pro-Russian separatists in eastern Ukraine claimed Saturday to have fulfilled their end of a February deal with government forces to withdraw heavy weapons from the frontline as part of a ceasefire.

"Today is the last day of the weapons withdrawal," Eduard Basurin, one of the rebel leaders told reporters in the town of Snizhne, where the separatists displayed eight 120mm mortars that had been moved back from their positions.

Watched by six international monitors, who declined requests for comment, the separatists towed the arms to a disused brick factory serving as an arms depot, about 90 kilometres (55 miles) from the rebel hub of Donetsk.

Basurin said the separatists were withdrawing a total of 26 mortars. "They will be stored with the rest of the military hardware," he said.

An AFP journalist saw four other artillery pieces inside the Snizhne depot.

Under the terms of the European-brokered, Russian-backed truce signed in the Belarussian capital Minsk on February 12, both sides to Ukraine's 11-month conflict must move their artillery back far enough to create a buffer zone of between 50 and 140 kilometres, depending on the weapons' range.

The process has been fraught with distrust and mutual recriminations, with both parties accusing the other of merely paying lip service to the peace deal.

Alexander Zakharchenko, the head of the self-proclaimed Donetsk People's Republic, accused Ukraine's government of failing to live up to its side of the agreement.

"We have fully removed heavy weapons from the line of contact. Ukraine has not yet done it," he told the separatist news agency DAN, threatening to redeploy the arms if Kiev did not match the deescalation.

- No dead or injured -

Ukrainian army spokesman Anatoliy Stelmakh assured that the government was upholding its end of the bargain, saying the army was continuing to withdraw its 220mm Uragan rocket launchers from the conflict zone, after earlier pulling back its smaller Grad multiple rocket systems.

"The process is ongoing," he said.

Ending the nearly-daily deluge of shelling and rocketing, which has killed over 6,000 people in eastern Ukraine since April 2014, would be a coup for German Chancellor Angela Merkel and French President Francois Hollande, architects of the Russian-backed ceasefire.

But ensuring that the big guns are being muzzled has proven tricky.

The Organization for Security and Co-operation in Europe, which is monitoring the truce, has recorded arms movements on both sides over the past two weeks but said it is being denied access to the information it needs to confirm weapons are being put beyond use.

Russia and Germany have called for the OSCE mission to double in strength, from its current tally of 452 observers to 1,000.

German Foreign Minister Frank-Walter Steinmeier, who was also in Riga, said he had received assurances from his Russian counterpart Sergei Lavrov that Moscow would work to ensure the observers received "guaranteed unlimited access"

After a blood-soaked start to the truce, which saw the rebels fight on to seize the transport hub of Debaltseve, eastern Ukraine has regained a measure of peace in the past two weeks.

Beyond the heavy weapons, the deal also calls for the withdrawal "of all foreign armed formations" and military equipment from Ukrainian territory -- an allusion to the accusations by Kiev and the West that Russia is arming and manning the conflict on the rebel side, which Moscow denies.

The accord also commits Kiev and the rebels to exchange all prisoners and to negotiate a change to Ukraine's constitution by the end of 2015, in order to give rebel-held areas more autonomy.

The pro-European government and pro-Kremlin separatists have a long road to travel before reaching that point.

On Saturday they again traded accusations of violating the ceasefire in the past 24 hours. But there was good news in Kiev.

"For the first time over the past few months" no Ukrainian soldier was killed or injured by rebel fire, a military spokesman said.