The Ukrainian government has accused pro-Russian rebels of tampering with evidence and restricting experts from assessing the Malaysia Airlines Flight 17 crash site.

On Wednesday, the passenger plane was carrying 298 people from 11 different countries when it was shot down from the sky by missiles and landed in the eastern Ukrainian region of Donetsk Ukraine, an area controlled by pro-Russia separatists.

Both the U.S. and Ukrainian government accuse rebels backed by the Russian government of firing the missile. However, Russia denies that it had any involvement in the crash or that it provided the rebels with sophisticated missile systems.

Although multiple world leaders have called for a transparent investigation, little progress has been made because investigators say separatists are limiting their access. A Ukrainian government spokesperson said that Ukrainian emergency personnel were able to find 186 bodies within 10 square miles, but the separatists restricted their access and were confiscating evidence.

"There are federal emergency service workers at the scene. ... But they have no freedom of movement. They are not allowed to leave the zone [under the control of the separatists]. The terrorists are taking all evidence that they gather," said Andriy Lysenko, the spokesman for the Ukrainian National Security and Defense Council, according to The Wall Street Journal.

Malaysian transport minister Liow Tiong Lai also expressed concern about the crash site, which he says "hasn't been properly secured." He said, "The integrity of the site has been compromised, and there are indications that vital evidence hasn't been preserved in place."

Investigators are trying to preserve critical evidence in order to determine what happened in addition to recover the black boxes, which store flight information and voice recordings between pilot and co-pilot.

Michael Bociurkiw, a spokesperson for the Organization for Security and Cooperation in Europe, said that the observers were still being denied access to certain areas and were initially met with hostility by rebels, reported CNN.

According to him, experts are collecting bodies and storing them in professional body bags.