On the ground, recovery experts began the grisly task of collecting remains of the 298 people killed two days earlier when a Malaysia Airlines jet exploded over the war zone of eastern Ukraine.

Across diplomatic channels, world leaders complained the recovery is not happening fast enough, mainly because pro-Russia militants control the crash site.

Dutch Prime Minister Mark Rutte urged Russian President Vladimir Putin to use his influence to force the rebels to allow full access.

"I want to see results in the form of unimpeded access and rapid recovery," Rutte said in a press briefing. "This is now priority number one."

Nearly two-thirds of the people on the jetliner, which was en route from Amsterdam to Kuala Lumpur, were Dutch.

Saturday brought a shift from the initial shock over the air disaster to the painstaking forensic and diplomatic challenges of figuring out what happened and how much the tragedy will escalate the Ukrainian conflict.

Masked gunmen at crash site

At the crash site, armed gunmen -- some of them masked -- kept close watch over a team of observers from the Organization for Security and Co-operation in Europe who gained access for a second day. Artillery fire reverberated in the distance.

Michael Bociurkiw, a spokesman for the OSCE group, told CNN that no security perimeter had been established and no one appeared to be in charge. While he said his monitors had better access than on Friday, observing about 75 body bags collected by civilian emergency workers, he described the situation as far from ideal for such a huge crime scene.

Meanwhile, international pressure increased on Russia to exert its influence over separatist rebels it supports who are fighting the Ukrainian government in the region.

European leaders including German Chancellor Angela Merkel and British Prime Minister David Cameron called on Putin to ensure free access to the crash site for a proper investigation.

Rutte called images of people rummaging through the debris and belongings of victims "downright disgusting."

'A very intense conversation'

Rutte told reporters of what he called "a very intense conversation" with Putin on Saturday in which he told the Russian leader "the opportunity expires to show the world that he is serious about helping."

Cameron, whose government summoned the Russian ambassador to urge more cooperation on the matter, said the European Union needs to reconsider its approach to Russia in light of evidence that the rebels fired the fatal missile.

Meanwhile, U.S. Secretary of State John Kerry spoke with his Russian counterpart, Foreign Minister Sergey Lavrov, to urge Moscow to get the rebels to stop fighting and talk peace, and also provide full access to the crash site.

The United States has said a surface-to-air missile fired from the rebel territory took down the Malaysia Airlines Boeing 777 with citizens from more than 10 nations aboard.

Russia has denied any involvement, and Putin said Ukraine's military campaign against the separatists was to blame. He also has called for a "thorough and objective investigation" of the crash.

Counter-accusations

Since the crash, the Ukrainian government and rebels have traded bitter accusations over who was responsible and what has been done since.

Vitaly Nayda, counterintellligence chief for Ukraine's Security Service, told reporters in Kiev that a Russian-made Buk M1 missile system had shot down the Malaysian airline.

He claimed that three Buk surface-to-air antiaircraft missile systems had crossed from Russia to Ukraine prior to the downing of Flight MH17, accompanied by Russian nationals who, he said, were the ones operating the sophisticated weaponry. All three Buk missile systems are no longer in Ukrainian territory, according to Nayda.

Prime Minister Arseniy Yatsenyuk, in an interview with CNN on Saturday, also suggested that whoever operated the missile system received expert training.

"This is not the Russian-led drunk terrorist who pressed the button," he said. "This is someone well-trained. Someone who knows how this machine works. Someone who has experience."

'Crime against humanity'