Pro-Russia separatists in eastern Ukraine are being accused of blocking the investigation into the apparent shooting-down of a Malaysian passenger jet with 298 people on board.

The accusations were made as observers from the Organisation of Security and Cooperation in Europe visited the site on Saturday, a day after they were asked to leave after being given limited access to the farmland where the jet went down.

Ukraine's government said that it had evidence Russia was helping pro-Moscow rebels cover up and destroy evidence from the crash site.

"Terrorists with the support of Russia are trying to destroy proof of this international crime," the government said in a statement, adding that rebels had removed 38 bodies and were blocking Ukrainian investigators.

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Al Jazeera's Scott Heidler, reporting from the crash site, said the separatists had established a 20sq/km safe zone where wreckage and many bodies are still lying uncovered in the open.

But with no safe corridor to the site from areas held by Ukraine, there were concerns about the safety of the monitors.

"If it's safe around here is one thing, but if it's safe to get here is the bigger issue," he said. "We don't know where exactly that fighting is going on but this is still an active battle area."

Before the OSCE team arrived, our correspondent reported seeing men with clipboards walking around as the first bodies were put into body bags by uniformed men. It was not known who they reported to.

For more than 40 hours, the site was not cordoned off, and public buses were still using a road going through the crash area.

Al Jazeera's Nazanine Moshiri, said the health minister of the self-declared Donetsk People's Republic said 38 passengers' bodies were in the morgue, but health authorities later said the bodies were not there.

"Officials are confirming things and denying things. If there are bodies there, it is a serious contravention of the site, it is tampering of a site which needs to be assessed by international monitors," she said.

Ukraine accuses separatists backed by Russia of shooting down the jet, and Vitaly Nayda, Ukraine's counter-intelligence chief, said: "We have compelling evidence that this terrorist act was committed with the help of the Russian Federation. We know clearly that the crew of this [missile] system were Russian citizens," Nayda said.

Malaysia has sent investigators to Ukraine, and Malaysia's transport minister said the country is "deeply concerned" that the crash site "has not been properly secured".

Liow Tiong Lai said "the integrity of the site has been compromised, and there are indications that vital evidence has not been preserved in place".

Source: Al Jazeera and agencies