Donetsk, Ukraine (CNN) -- 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.
Pressure on Putin
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."
'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."
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."
'Crime against humanity'
Ukraine and the international community "will find out all responsible for this international crime, and those who supported them, because this is (a) crime against humanity, and the building of (the) International Criminal Court is very big," Yatsenyuk added.
Even the local head of the rebels conceded for the first time Saturday that the plane got shot down. But Alexander Borodai reiterated that his forces did not do it. He told reporters the rebels lacked the firepower to hit an airplane so high up.
According to government officials, the rebels also removed debris and 38 bodies from the scene as part of an attempt to cover up what happened, and money, jewelry and other items had been looted from the dead. They urged relatives to cancel the credit cards of victims.
Borodai, the rebel leader who calls himself the prime minister of the self-styled Donetsk People's Republic, denied that his forces removed any bodies.
"There is even a house where a body fell, the landlord asked us to remove, and we haven't because we are not allowed to move anything," he said.
A CNN crew at the scene Saturday said it did not see any signs of looting or the rebels rummaging through items at the crash site.
Access an issue
The fields where the plane came down Thursday, near the town of Torez in the Donetsk region, are in a volatile rebel-controlled area, making access to the scattered debris, bodies and body parts difficult.
Ukrainian officials blamed the security issues on factionalism and lack of internal communication among the pro-Russian rebels.
Some rebel groups in the area have agreed to give OSCE experts access to the wreckage, while others have not, a spokesperson for Donetsk Gov. Oleksandr Omelchenko said. He said the conditions make it impossible to know whether all the armed rebels have left an area.
This is consistent with what CNN journalists have seen at the debris field. Earlier Saturday, a rebel commander on the ground gave a group of CNN journalists permission to approach the wreckage, but within 30 minutes warning shots were heard and the journalists were told to leave.
One key issue for investigators is the location of the plane's flight data recorders, which may hold crucial data.
The Ukrainian government said Friday that the so-called black boxes are still in Ukrainian territory but didn't clarify whether they were in Ukraine's possession.
Bociurkiw of the OSCE said no one at the crash site was able to tell his people where the recorders might be.
Malaysian investigators also touched down in Kiev on Saturday to try to get the bottom of what happened to the jetliner.
But Malaysia's official news agency Bernama said they were still negotiating with pro-Russian rebels over access for their 131-member team.
Malaysian Transport Minister Liow Tiong Lai said Saturday in Kuala Lumpur that Malaysia was "deeply concerned that the crash site has not yet been properly secured."
"There are indications that vital evidence has not been preserved in place," he said.
The full list of the passengers was released Saturday. According to a final breakdown from Malaysia Airlines, 193 of those killed were from the Netherlands, including one who had dual U.S.-Dutch citizenship.
There were also 43 victims from Malaysia, including the plane's 15 crew; 27 from Australia; 12 from Indonesia; 10 from the United Kingdom, including one who had dual UK-South African citizenship; four each from Germany and Belgium; three from the Philippines and one each from Canada and New Zealand.
Eighty of the victims were children, the United Nations said.
In the Netherlands, dozens of police officers are now visiting all the families of the victims. They will gather specific information that will help identify the victims, such as DNA samples, details of tattoos and dental records, Dutch police said. A Dutch forensics team has already arrived in Ukraine.
The FBI is sending two investigators to work on the case, a U.S. law enforcement official said, but the Ukraine government will be in charge of the investigation.
Australia is sending six foreign affairs officers to Kiev to assist in the investigation, the country's Prime Minister Tony Abbott said Saturday.
The Kremlin has criticized Abbott over his harsh words on possible Russian involvement in the tragedy. He repeated them Saturday.
"Australia takes a very dim view of countries which facilitate killing of Australians, as you'd expect us to. We take a very, very dim view of this and the idea that Russia can wash its hands of responsibility, because this happened in Ukrainian airspace, just does not stand serious scrutiny," Abbott said.
Obama's focus on Russia
U.S. President Barack Obama also said Russia likely bears some of the responsibility, noting rebel fighters couldn't have operated the surface-to-air missile "without sophisticated equipment and sophisticated training, and that is coming from Russia."
A day before MH17 came down, Obama announced expanded sanctions against a number of major Russian companies in response to Russia's actions in Ukraine.
In an apparently retaliatory move, Russian Foreign Ministry spokesman Alexander Lukashevich said Saturday that Russia had added the names of 13 American citizens to a list that bans them from entering Russia. The list includes U.S. Rep. Jim Moran, D-Virginia.
CNN's Phil Black reported from Donetsk and Laura Smith-Spark reported and wrote from London and Tom Cohen reported and wrote from Washington. CNN's Nic Robertson, Ivan Watson, Barbara Starr, Elise Labott, Pam Brown, Jim Sciutto, Brian Walker, Ralph Ellis, Paul Ferguson and Antonia Mortensen also contributed to this report, as did journalists Victoria Butenko and Azad Safarov.