Two days after the tragic crash of Malaysia Airlines Flight MH17, investigators continue struggle to gather evidence on how the plane crashed. Both sides, the Ukrainian government and the rebels, blame the other for the lack of progress.

The Boeing 777 airliner was carrying 298 passengers and crew when it was shot down over eastern Ukraine on July 17. Blame has been thrown around, and many nations agree that investigations are necessary.

However, the location of the crash site has complicated the process.

Having fallen on rebel-held territory, pro-Russian rebels, the same who Kiev blames for the incident, control the area and have prevented Ukrainian government investigators from moving freely around the site, according to the Wall Street Journal.

Those present at the site report that rebels have not enforced any security area and have been removing debris from the crash site, potentially contaminating any retrievable evidence. This has caused some countries, like Malaysia, to worry about how secure the area is, reports the Journal.

"The integrity of the site has been compromised, and there are indications that vital evidence hasn't been preserved in place," Malaysia's transportation minister said.

Another problem has been the removal of bodies. The Washington Post reported that the Ukrainian government alleges pro-Russian separatists have begun removing bodies from the site. Saturday night, rebels moved 37 bodies to a hospital in the rebel stronghold of Donetsk in order to conduct their own investigation.

"Russian-led terrorists are preventing access of the international community and foreign governments to the location where MH17 crashed," Ukrainian Prime Minister Arseniy Yatsenyuk said.

The rebels, on the other hand, argue that the crash site is well protected.

According to the Washington Post, Andrei Purgin, a top rebel leader, said the site was "under the reliable protection of the armed forces of the Donetsk People's Republic" but failed to provide specifics on what happened to the bodies.

However, Ukraine's worries concerning the crash and the manipulation of evidence extend past the crash site. The Los Angeles Times explained that Ukraine alleges three Buk missile systems crossed the border into Russia between 2 a.m. and 4 a.m. Friday morning. The information comes from Vitaly Nayda, Ukraine's counter-intelligence chief, speaking with reporters in Kiev.

One of the missile systems had a missile missing, Ukrainian government officials said, citing a video. If these allegations prove to be true, it could implicate Russia in the airliner disaster, which Moscow denies.

Meanwhile, the U.S. government has begun attempts to link the pro-Russian separatists to MH17's crash, according to The Associated Press. Both President Obama and U.S. ambassador to the U.N., Samantha Power, have called for an international investigation into the matter.