MH17 site search resumes

Grabove - International experts pushed on Saturday with their painstaking probe at the crash site of downed flight MH17 in east Ukraine after US President Barack Obama called on Russia to heed international pressure to defuse the civil war tearing apart its neighbour.

Some 70 Dutch and Australian police experts were back for a second day scouring the vast scene with sniffer dogs for more human remains, while those leading the investigation have warned the grim task could take some three weeks to complete.

The shooting down of the Malaysia Airlines plane more than two weeks ago, killing all 298 people on board, refocused world attention on the conflict in Ukraine and pushed the United States and European Union into imposing the toughest sanctions against Moscow since the end of the Cold War.

Washington accuses insurgents of blowing the airliner out of the sky with a surface-to-air missile likely supplied by Russia, while Moscow and the rebels have pointed the finger at the Ukrainian military.

In a telephone call with Russian leader Vladimir Putin, Obama expressed his "deep concerns" about Moscow's increased support for separatists rebels waging a brutal conflict against Kiev that has claimed more than 1 150 lives.

"Right now what we've done is impose sufficient costs on Russia that, objectively speaking, President Putin should want to resolve this diplomatically, to get these sanctions lifted, get their economy growing again, and have good relations with Ukraine," Obama told an impromptu news conference.

"But sometimes people don't always act rationally", he added.

Separately, the Kremlin said the two leaders had agreed that the current standoff in Ukraine, where pro-Russian rebels are battling government forces was "not in the interest of either country".

But Putin lashed out at the latest economic sanctions as "counterproductive, causing serious damage to bilateral cooperation and international stability overall," the Kremlin said.

'Long, slow process'

Australian Prime Minister Tony Abbott welcomed the recovery of more remains from the crash site after a bulk of the investigators managed for the first time Friday to reach the site after being thwarted by days of clashes between government troops and rebel fighters.

More than 220 coffins have already been sent back to the Netherlands, which lost 193 citizens in the 17 July crash, but more body fragments remain lying out in the cornfields where the plane came down.

"It is good that, we've had, for the first time, large numbers of Australian and Dutch police on site, large numbers of investigators on site who have been able to begin a thorough, professional search", Abbott told reporters in Sydney.

But he warned that probe at the crash site covering 20km2 would be "a long and slow process".

Even as the international team managed to begin work at the site, the fighting that had impeded their probe continues to rage across eastern Ukraine.

Ukraine's military said that overnight its positions across the region had continued to come under rocket, tank and mortar fire.

No new casualties were reported but an ambush some 24 hours earlier in a town 25km from the MH17 site left 14 people dead, including at least 10 soldiers.

Government forces have made major gains over the past month and say they are getting close to cutting off the main rebel stronghold of Donetsk from the Russian border and a second insurgent bastion of Lugansk.

Despite mounting losses, Kiev's bullish top brass have pledged to stamp out the insurgency in time for early parliamentary polls expected in the next few months, and reiterated calls for insurgents to lay down their arms.

"All those who want to leave Ukrainian towns and villages still have the possibility to run back to Russia", Ukraine's army chief Valeriy Geletey said in televised comments.

"Believe me they are fleeing. We are getting calls saying 'let us leave the towns'", he said.

But analysts warn that fighting is unlikely to end soon, with rebel fighters hunkering down in major cities and pledging to fight to the death.

And some EU diplomats have warned that recent sanctions could actually embolden Putin by convincing him he has nothing to lose now by going all-in over the Ukraine crisis.

Stoking those fears, Pentagon spokesman Rear Admiral John Kirby said Russia was continuing to reinforce its military presence along the border with Ukraine.

US Vice President Joe Biden, meanwhile, announced the United States was giving Ukraine $8m in new aid for the nation's border guards.