GRABOVE, Ukraine : - International experts pushed on Saturday with their painstaking probe at the vast crash site of downed flight MH17 in eastern Ukraine, deploying sniffer dogs to help find any remains still left at the scene.Some 70 Dutch and Australian police investigators were back for a second day to scour through the wreckage, while those leading the hunt have warned the grim task could take some three weeks to complete. An AFP journalist, asked by the probe team to remain a few hundred metres from the investigators, saw search crews fanning out across a field and occasionally bending down to collect and bag objects. A refrigerated ambulance van was on site to store any remains found, while armed rebel fighters kept an eye on the gathered journalists. 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 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 on Friday, US President Barack 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 since mid-April. ‘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. The Kremlin said the two leaders had agreed that the 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. 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 July 17 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.But he warned that the probe at the crash site covering 20 square kilometres (eight square miles) 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 its positions across the region came under heavy fire overnight and that separatists had hit an army drone with a missile similar to the one they say downed MH17. No new casualties were reported but an ambush some 24 hours earlier in a town 25 kilometres (15 miles) 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. The conflict has taken a heavy toll on civilians across the region and the mayor in the besieged industrial hub of Lugansk warned that the city was ‘on the verge of a humanitarian catastrophe’ as electricity failed and water and fuel ran low. Kiev’s top brass have pledged to stamp out the insurgency in time for early parliamentary polls expected in the next few months, and have offered to let rebels ‘run back to Russia’ if they lay down their arms. 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, the Pentagon said Russia was continuing to reinforce its military presence along the border with Ukraine.