The remains of the last nine victims of flight MH17 may never be recovered from the Ukrainian battlefield where their plane was downed four months ago, the Dutch foreign minister says.

Bert Koenders made the grim assessment in the city of Kharkiv, where he attended a memorial service for five more sets of human remains collected from the site of the disaster and flown to The Netherlands.

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Another ceremony attended by some 1,600 friends and relatives was planned to take place in The Netherlands on Monday.

“We cannot say at this moment in any certain way… at what moment, and even if, we can recover the last nine” victims, he said of the air crash that killed all 298 on board, including 193 Dutch.

The shooting down of the Malaysia Airlines Boeing 777 on July 17 was one of the worst tragedies of a war in which an estimated 4,000 people have died. So far, the remains of 289 of those victims have been identified.

Ukraine and the West blame Russian-backed separatist fighters using surface-to-air missiles for the catastrophe, while Moscow has pointed the finger at Kiev’s forces, in an incident that galvanised international shock over the chaos in a country bordering the European Union.

The fighting is continuing in the Ukraine’s industrial east despite a two-month-old ceasefire deal, stopping rescuers from getting to the remains of victims.

Two tanks and two armoured fighting vehicles could be seen on the outskirts of the city, while rebels were digging trenches.

“These are our armoured vehicles changing position to escape the firing by the Ukrainians,” said Zoya, a local resident who was coming to check on her house which she’d been forced to abandon for a safer location with friends elsewhere in the city.

Russia, which annexed Ukraine’s Crimea region in March and lends close political and humanitarian support to the separatist areas in the east, denied the latest Ukrainian allegation that it was dispatching regular troops to join the fighting.

Ukraine’s military made headlines around the world on Friday with the claim that columns of hardware, including 32 tanks, had poured across the border which is under the control of Russia and the pro-Russian rebels.

However, Foreign Minister Sergei Lavrov laughed off the allegation after US State Department spokeswoman Jen Psaki said she had no “independent confirmation” of the report.

“If Psaki doesn’t have it, I don’t,” Lavrov told journalists with a chuckle in Beijing, where he met his US counterpart John Kerry ahead of an APEC summit.

A flurry of diplomatic activity is approaching, with the APEC summit in China and a Group of 20 meeting in Australia next week, where President Vladimir Putin will have the chance to put his case before world leaders.

Speaking in Beijing, Lavrov appeared to soften Russia’s position, saying that US involvement in attempts to resolve the crisis would be a “step in the right direction”.