 -- Wreckage from the downed Malaysia Airlines plane in Ukraine has been “significantly altered,” international monitors told ABC News today, as remains of the victims arrived in territory held by the Ukrainian government.

Major pieces of the front of the plane appear to have been cut away, said Michael Bociurkiw, a spokesman for the Organization for Security and Cooperation in Europe, the group observing the crash site. Earlier, investigators observed someone using power tools to cut into the wreckage.

Rebels have said they had to move and alter big pieces to get at bodies and body parts. But the OSCE said what they saw was a “very invasive” altering of the wreckage.

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The crash site itself, in farmland held by the pro-Russian separatists who the West accuses of shooting down the plane, remained unsecured five days after the disaster -- another source of frustration for officials around the world eager to establish the facts of the case.

A refrigerated train carrying the bodies pulled into a station in Kharkiv, a government-controlled city where Ukrainian authorities have set up their crash investigation center. Government spokesman Oleksander Kharchenko said Ukraine "will do our best" to send the bodies to the Netherlands today. Of the 298 people who died aboard the Amsterdam-to-Kuala Lumpur flight, 193 were Dutch citizens.

The black boxes from the downed plane were handed over to Malaysian officials Monday.

In Brussels, European Union foreign ministers were discussing whether to impose more sanctions in response to the disaster. Europe and the United States have imposed targeted economic sanctions against Russia for supporting Ukraine's five-month insurgency that began after pro-Russian President Viktor Yanukovych was ousted by protesters in February.

The rebels control a swath of territory in two eastern provinces, and have battled Ukrainian troops with heavy weapons including tanks and missile launchers that the West says came from Russia. Russia denies supporting the insurgency.

The sanctions so far have focused on individuals instead of entire sectors of the economy, though the EU already was moving to broaden them before the downing of the plane. British Prime Minister David Cameron said Monday that the jet's destruction on Thursday drastically changed the situation, and that the Russians cannot expect continued access to European markets and capital if they continue to fuel a war against another European country.

Lithuanian Foreign Minister Linas Linkevicius blamed "terrorists supplied by Moscow" for shooting down the airliner, killing all aboard. He said he hoped the EU would impose beefed-up sanctions on Russia. His call for an arms embargo was a direct challenge to France, which was building two warships for the Russian navy.

At the crash site near the village of Hrabove, a few rebel fighters accompanied observers from the Organization for Security and Cooperation in Europe. The farmland where the wreckage is scattered was otherwise unguarded and unsecured. Even the red-and-white tape that had sealed off the fields was torn away.

In some places, the smell of decay and flies suggested the presence of remains under the wreckage, and observers said Monday that not all bodies had been recovered.

About 70 villagers, most of them older women wearing headscarves, gathered across the road from the site to sing Ukrainian Orthodox hymns at a memorial service led by several black-robed priests.

The Associated Press contributed to this report.