Last Updated Jul 21, 2014 8:55 PM EDT
TOREZ, Ukraine - Bowing to international pressure Monday, pro-Moscow separatists released a train packed with bodies and handed over the black boxes from the downed Malaysia Airlines plane, four days after it plunged into rebel-held eastern Ukraine.
CBS News confirmed that the flight data recorders from Malaysia Airlines Flight 17 have been turned over to Malaysian officials.
With body parts decaying in sweltering heat and signs that evidence at the crash site was mishandled, anger in Western capitals has mounted at the rebels and their allies in Moscow. Their reluctant cooperation will soothe mourning families and help investigators, but may do little to reconcile the East-West powers struggling over Ukraine's future.
The bodies of the 298 victims, most from the Netherlands, have become a part of the conflict in Ukraine because they could hold evidence of what brought the plane down on July 17 as it was flying from Amsterdam to Kuala Lumpur.
The train departure came hours after the Malaysian prime minister announced Monday that an agreement has been reached with the Russian-back separatists in eastern Ukraine over access to the Malaysia Airlines Flight 17 crash site, and to the bodies of the victims.
In a statement, Prime Minister Najib Razak said that, "under difficult and fluid circumstances," an agreement has been reached with Alexander Borodai -- the rebel leader in charge of the region where the plane went down -- for access to the victims' remains and the plane's "black box" data and voice recorders.
According to Razak, the separatists agreed to move the remains of 282 people currently in Torez, by train, to Kharkiv, where they will be handed over to representatives from the Netherlands. The bodies of 16 victims have not been recovered.
The Ukrainian government is hoping the train will go to the government-controlled eastern city of Kharkiv, where it has set up a crash crisis center, but the rebels have not confirmed the train's destination.
Razak also said that the two black boxes will be handed over to Malaysian officials in Donetsk this evening, which CBS learned did happen.
Safe access to the crash site will also be guaranteed to independent international investigators, so that they may begin a full investigation.
"I ask that all parties continue to work together to ensure that this agreement is honored," said Razak. "Only then can the investigation into MH17 truly begin; only then can the victims be afforded the respect they deserve. We need to know what caused the plane to crash, and who was responsible for it, so that justice may be done."
On Sunday, Razak had said the remains of the Malaysian victims must be returned to Malaysia before the Eid al-Fitr, which marks the end of the Muslim fasting month of Ramadan. This year, it falls on July 28.
Four days after Flight 17 was shot out of the sky, international investigators still have had only limited access to the crash site, hindered by the pro-Russia fighters who control the verdant territory in eastern Ukraine. Outrage over the delays and the possible tampering of evidence at the site was building worldwide, especially in the Netherlands, where 192 of the plane's 298 victims were Dutch and another was Dutch-American.
On Monday, Associated Press journalists said the smell of decay was overwhelming at the train station in the rebel-held town of Torez, where the remains have been kept in parked, refrigerated train cars. Many of the inspectors wore masks or pressed cloths to their faces on the sunny, 84-degree Fahrenheit day.
Earlier, a Ukrainian train engineer told the AP that a power outage had hit the cars' refrigeration system for several hours overnight but was back up early Monday.
The investigators led by Peter Van Vilet of the Dutch LTFO forensic office stood for a moment with their heads bowed and hands clasped before climbing aboard to inspect the train cars, surrounded by armed rebels.
"I think the storage of the bodies is of good quality," Van Vilet said. "We got the promise the train is going."
In Kharkiv, another team of international experts arrived, including 23 Dutch, three Australians, two Germans, two Americans and one person from the United Kingdom.
Fighting flared again Monday between the separatists and government troops in the eastern rebel-held city of Donetsk, just 30 miles to the west of the crash site. City authorities said battles were taking place near the town's airport. An AP reporter heard several explosions and saw smoke rising from that direction.
Fighting began in mid-April between the government and the Russian-speaking separatists in eastern Ukraine after Russia annexed Ukraine's Crimean Peninsula a month earlier.
Pressure has been growing on Russian President Vladimir Putin - who the U.S. and others say has backed and armed the rebels - to rein in the insurgents and allow a full-scale investigation into the downing of the plane.
Russia has denied backing the separatists.
The U.N. Security Council unanimously adopted a resolution Monday demanding international access to the site of the downed plane in Ukraine and an end to military activities around the area, following intense pressure on a reluctant Russia to support the measure. The resolution calls for a "full, thorough and independent international investigation" into the downing of Malaysia Airlines Flight 17 in Hrabove. All 15 council members voted in favor of the Australia-proposed measure in a televised meeting.
The resolution also demands that those responsible for the incident be held to account, although it lacks enforceability, CBS News' Pamela Falk reported from the U.N.
In speaking on the incident, many nations' representatives made the point that supporting militant insurgents may have had tragic consequences, and several implicitly blamed Russia for the support of the rebel groups who control the territory where the plane was brought down.
In Britain, Prime Minister David Cameron said he hoped Russia will support the Security Council resolution.
"We would hope that, given what has happened, there would be unanimous support behind the principle of unfettered access to those who have the task of identifying and repatriating the victims, as well as to the investigators," Cameron's spokesman said.
The United States has presented what it called "powerful" evidence that the rebels shot down the Boeing 777 with a Russian surface-to-air Buk missile. That evidence included video of a rocket launcher, one surface-to-air missile missing, leaving the likely launch site; imagery showing the firing; phone calls claiming credit for the missile strike and phone recordings said to reveal a cover-up at the crash site.