Fighting and artillery barrages flared near the Russian border in the hours after President Barack Obama called the loss of flight MH17 a "wake-up call" to Europe to join the United States in threatening Moscow with heavier economic sanctions if it does not use its influence to help end a conflict that has driven the gravest East-West confrontation since the Cold War.

Malaysia, whose national airline has been battered by its second major disaster this year, said it was "inhumane" to bar access to the site around the village of Hrabove, near the city of Donetsk, and said Russia was doing its "level best" to help. It defended the use of an air corridor over Ukraine's war zone.

"The terrorists, with the help of Russia, are trying to destroy evidence of international crimes," the Ukrainian government said in a statement. "The terrorists have taken 38 bodies to the morgue in Donetsk," it said, accusing people with "strong Russian accents" of threatening to conduct autopsies.

Ukraine's prime minister said armed men barred government experts from collecting evidence and threatened to detain them.

 At Hrabove, one armed man from the separatist forces told Reuters that bodies had been taken away in trucks. Amid reports of looting, militants and local people say they have been doing their best to collect evidence and preserve human remains.

As the stench of death begins to pervade the area, a Reuters correspondent watched rescue workers carry bodies across the fields and gather remains in black sacks. One local resident said Ukrainian fighter jets had flown over the area earlier.

THREATS

Quite who controls what around the site is unclear. Rebel forces, who have declared a Donetsk People's Republic in the Russian-speaking east and want union with Moscow, have set up cordons and checkpoints around the area.

The security council in Kiev said staff of the emergencies ministry had found 186 bodies - a little more than half the 298 aboard the Malaysia Airlines Boeing 777 - and had checked some 18 sq.km (7 square miles) of the scattered 25-sq.km crash site. But the workers were not free to conduct a normal investigation.

 "The fighters have let the Emergencies Ministry workers in there but they are not allowing them to take anything from the area," security council spokesman Andriy Lysenko said. "The fighters are taking away all that has been found."

He added that he had no information on the black box flight recorders, both of which separatists have said have been found.

A party of observers from Europe's OSCE security body, based in Donetsk, visited the site on Friday and found access limited by what it said were hostile armed men, some of them drunk.

Following a demand from the United Nations Security Council for an independent investigation, both sides in the conflict have offered ceasefires and cooperation but the situation on the ground remains confused and Ukrainian officials said there were several clashes overnight in areas near the city of Luhansk.

A team of Malaysian experts flew in to Kiev on Saturday.

 Ukrainian Prime Minister Arseny Yatseniuk issued a statement after he spoke to the foreign minister of The Netherlands - more than half those aboard the flight from Amsterdam were Dutch.

He said government experts sent to the site "were not given the opportunity to collect evidence".

"They gave them less than an hour there, and made them leave the site of the catastrophe threatening to take them hostage."

WAKE-UP CALL

With some commentators talking of a pivotal moment in the East-West confrontation over Ukraine that began in November, Obama said the shooting down of MH17 in a region controlled by Russian-backed separatists should be a "wake-up call for Europe and the world" - an indication of some U.S. impatience at worry among EU allies that challenging Moscow could hurt their trade.

 While stopping short of blaming Russia for Thursday's loss of the plane, three hours into a flight from Amsterdam to Kuala Lumpur, he said it was the Kremlin's failure to stop the violence that made it possible to shoot down the plane.

A senior U.S. official said there was increasing confidence that the missile was fired by separatist, as the Ukrainian government asserts, and that there was no reason to doubt the validity of a audiotape that Kiev has circulated in which voices identified as separatists discussed the downing of the plane.

"This certainly will be a wake-up call for Europe and the world that there are consequences to an escalating conflict in eastern Ukraine; that it is not going to be localized, it is not going to be contained," Obama told reporters on Friday.

Obama spoke by phone later with German Chancellor Angela Merkel, British Prime Minister David Cameron and Australian Prime Minister Tony Abbott. The White House said they discussed Ukraine and the downed jet and the need for an unimpeded international investigation into what happened.

Malaysian Transport Minister Liow Tiong Lai said on Saturday he would fly to the Ukraine capital of Kiev to ensure an investigating team gets safe access to the site. Before setting off, he said it would be "inhumane" not to have access, but said Moscow was trying to help: "They are trying their level best to assist Malaysia to ensure we have a safe site," Liow said.