Nobody knows how many bodies from the Malaysia Airlines Flight 17 crash have been moved, where they were taken or exactly who moved them, the spokesman for a group of international observers told CNN on Saturday.

Michael Bociurkiw of the Organization for Security and Co-operation in Europe told "Erin Burnett OutFront" the group went to the crash site in a remote section of eastern Ukraine on Saturday and saw men moving an unknown number of body bags.

It's hard to get reliable information because several groups of pro-Russian separatists -- some of them masked -- control the area, he said. "But there doesn't seem to be one commander in charge."

Separatists are suspected of shooting down the plane with a Russian-made surface-to-air missile on Thursday.

Three air crash investigators from Ukraine accompanied the OSCE observers but didn't have much time to do their work, he said. "They need a lot more time and a lot more freedom of access," Bociurkiw said.

More world powers have deplored the situation and asked Russian President Vladimir Putin to use his influence on the separatists.

"Yesterday, the [OSCE] monitors were allowed only 75 minutes at the site," the U.S. State Department said in a statement released Saturday night. "Today, they were allowed less than three hours. ...

"The site is not secure, and there are multiple reports of bodies being removed, parts of the plane and other debris being hauled away, and potential evidence tampered with. This is unacceptable and an affront to all those who lost loved ones and to the dignity the victims deserve."

British Prime Minister David Cameron wrote a Sunday Times op-ed piece urging Putin to somehow make the crash site more accessible and calm the strife between Ukraine and the separatists. German Chancellor Angela Merkel and Dutch Prime Minister Mark Rutte spoke out as well.

"I want to see results in the form of unimpeded access and rapid recovery," Rutte said in a press briefing. Nearly two-thirds of the people on the jetliner, which was en route from Amsterdam to Kuala Lumpur, were Dutch.

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

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."

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 Russian-made surface-to-air missile fired from the rebel territory took down the Malaysia Airlines Boeing 777 with citizens from more than 10 nations aboard.

The missile systems are the size of tanks, have treads like tanks and weigh around 50 tons. They require large, specialized military vehicles to transport them.

U.S. officials believe the missile systems may have been moved back across the border into Russia, CNN foreign affairs reporter Elise Labott said Saturday.

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.

Since the crash, the Ukrainian government and rebels have traded bitter accusations over who was responsible and what has been done since. Ivan Watson, a CNN international reporter, called it "an information war."

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."

(CNN)