(Adds U.N. draft resolution, paragraphs 3-4)
* Ukraine says rebels hamper access to crash site
* Rebels say Kiev dragging its feet, black boxes not found
* Ukraine says experienced Russian crew fired fatal missile
* Kerry's spokesman says access denial "unacceptable"
By Anton Zverev and Peter Graff
HRABOVE/DONETSK, Ukraine, July 20 (Reuters) - Ukraine accused Russia and pro-Moscow rebels on Saturday of destroying evidence to cover up their guilt in the shooting down of a Malaysian airliner that has intensified a showdown between the Kremlin and Western powers.
As militants kept international monitors away from wreckage and scores of bodies festered for a fourth day on Sunday, Russian President Vladimir Putin urged the rebels to cooperate and insisted that a U.N.-mandated investigation must not leap to conclusions. Moscow denies involvement and has pointed a finger at Kiev's military.
The U.N. Security Council was considering a draft resolution to condemn the attack, demand armed groups allow access to the crash site and call on states in the region to cooperate with an international investigation.
Australia - which lost 28 citizens - circulated a draft text, seen by Reuters, to the 15-member Security Council late on Saturday and diplomats, speaking on condition of anonymity, said it could be put to a vote as early as Monday.
The Netherlands, whose citizens made up most of the 298 aboard MH17 from Amsterdam en route to Kuala Lumpur, said it was "furious" about the manhandling of corpses strewn for miles over open country and asked Ukraine's president for help to bring "our people" home.
U.S. President Barack Obama said the loss of the Malaysia Airlines flight showed it was time to end the Ukraine conflict and Germany called it Moscow's last chance to cooperate.
European powers seemed to swing behind Washington's belief Russia's separatist allies were to blame. That might speed new trade sanctions on Moscow, without waiting for definitive proof.
"He has one last chance to show he means to help," Dutch Prime Minister Mark Rutte said after a telephone call to Putin.
Britain, which lost 10 citizens, said further sanctions were available for use against Russia. Prime Minister David Cameron, writing in The Sunday Times, said European countries should make their power count. "Yet we sometimes behave as if we need Russia more than Russia needs us."
German Chancellor Angela Merkel, the most powerful figure in the EU, spoke to Putin on Saturday, urging his cooperation. Merkel's foreign minister, Frank-Walter Steinmeier, told Bild am Sonntag newspaper: "Moscow may have a last chance now to show that it really is seriously interested in a solution."
"Now is the moment for everyone to stop and think to themselves what might happen if we don't stop the escalation."
Germany, reliant like other EU states on Russian energy and more engaged in Russian trade than the United States, has been reluctant to escalate a confrontation with Moscow that has revived memories of the Cold War. But with military action not seen as an option, economic leverage is a vital instrument.
Russia said on Saturday it was retaliating against sanctions imposed by the United States last week, before the air disaster, by barring entry to unidentified Americans and warned of a "boomerang effect" on U.S. business. But Foreign Minister Sergei Lavrov and U.S. Secretary of State John Kerry agreed in a phone call to try to get both sides in Ukraine to reach a consensus on peace, Russia's Foreign Ministry said.
The U.S. State Department, however, put the onus on Russia, saying Kerry urged Russia to take "immediate and clear actions to reduce tensions in Ukraine".
Driving home its assertion that the Boeing 777 was hit by a Russian SA-11 radar-guided missile, Ukraine's Western-backed government said it had "compelling evidence" the battery was not just brought in from Russia but manned by three Russian citizens who had now taken the truck-mounted system back over the border.
The prime minister, denying Russian suggestions that Kiev's forces had fired a missile, said only a "very professional" crew could have brought down the speeding jetliner from 33,000 feet (10,000 metres) - not "drunken gorillas" among the ill-trained insurgents who want the Russian-speaking east to be annexed by Moscow.
The Wall Street Journal reported that U.S. intelligence assessments indicated that Moscow likely provided rebels with sophisticated anti-aircraft systems in recent days.
The Journal cited U.S. officials as saying they now suspect that Russia supplied the rebels with multiple SA-11 systems by smuggling them in with other equipment, including tanks.
Fighting flared in eastern Ukraine on Saturday. The government said it was pressing its offensive in the east.
Observers from Europe's OSCE security agency visited part of the crash site near the village of Hrabove for a second day on Saturday and again found their access hampered by armed men from the forces of the self-declared People's Republic of Donetsk. An OSCE official said, however, they saw more than on Friday.
At one point, a Reuters correspondent heard a senior rebel tell the OSCE delegation they could not approach the wreckage and would simply be informed in due course of an investigation conducted by the separatists. However, fighters later let them visit an area where one of the airliner's two engines lay.
"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 had barred government experts from collecting evidence.
Kerry told Lavrov the United States was "very concerned" over reports that the remains of victims and debris had been removed or tampered with, the State Department said. He said Washington was also concerned over denial of "proper access" for international investigators and OSCE monitors.
"This is unacceptable and an affront to all those who lost loved ones and to the dignity the victims deserve," Kerry's spokeswoman, Jen Psaki, said in a statement. "We urge Russia to honour its commitments and to publicly call on the separatists to do the same."
Ukrainian President Petro Poroshenko urged the United Nations to label rebels fighting his forces in the eastern regions of Luhansk and Donetsk as belonging to "terrorist organisations".
In the regional capital Donetsk, the prime minister of the separatist authorities told a news conference that Kiev was holding up the arrival of international experts whose mission to investigate the cause - and potentially blame - for the disaster was authorised on Friday by the U.N. Security Council.
Contrary to earlier statements by the rebels, Alexander Borodai said they had not found the black box flight recorders. He said rebels were avoiding disturbing the area.
"There's a grandmother. A body landed right in her bed. She says 'please take this body away'. But we cannot tamper with the site," Borodai said. "Bodies of innocent people are lying out in the heat. We reserve the right, if the delay continues ... to begin the process of taking away the bodies. We ask the Russian Federation to help us with this problem and send their experts."
At Hrabove, one armed man from the separatist forces told Reuters that bodies had already been taken away in trucks. Another said people had looted valuables immediately after the crash. But fighters and local people say they have been doing their best to collect evidence and preserve human remains.
As the stench of death began to pervade the area after Thursday's crash, correspondents watched rescue workers carry bodies across the fields and gather remains in black sacks.
The Ukrainian security council in Kiev said staff of the Emergencies Ministry had found 186 bodies and had checked some 18 sq km (seven square miles) of the scattered 25-sq-km (10-square-mile) 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."
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, but said Russia was doing its "level best" to help.
A team of Malaysian experts flew in to Kiev on Saturday and experts from Interpol are due there on Sunday to help with the identification of victims. Dutch, U.S. and other specialists are being lined up to help in the investigation.
"Any actions that prevent us from learning the truth about what happened to MH17 cannot be tolerated," Malaysian Transport Minister Liow Tiong Lai said on Saturday before leaving for Kiev. "Failure to stop such interference would be a betrayal of the lives that were lost."
The deadliest attack on a commercial airliner follows the disappearance of Malaysia Airlines' Flight MH370 in March with 239 passengers and crew.
The scale of the disaster could prove a turning point for international pressure to resolve the crisis in Ukraine, which has killed hundreds since pro-Western protests toppled the Moscow-backed president in Kiev in February and Russia annexed the Crimea peninsula a month later. (Additional reporting by Pavel Polityuk and Elizabeth Piper in Kiev, Peter Graff in Donetsk, Anuradha Raghu, Trinna Leong and Yantoultra Ngui in Kuala Lumpur, Costas Pitas in London, Eric Beech in Washington and Michelle Nichols in New York; Writing by Alastair Macdonald; Editing by Andrew Heavens, Sonya Hepinstall, Nick Macfie and Paul Tait)