The Organisation for Security and Cooperation in Europe (OSCE) already has observers in eastern Ukraine. A team of 25 observers tried on Friday to gain access to the crash site, which stretches over several kilometers. The area is controlled by pro-Russian separatists who had previously agreed to allow access. The OSCE said there were indications that debris and material had been moved and the site had not been sealed off.

The United Nations and world leaders have called for a rapid investigation into the shooting down of the Malaysia Airlines Boeing 777 flight from Amsterdam to Kuala Lumpur on Thursday. All 298 people on board were killed. The US and Britain said a surface-to-air missile appeared to have been fired from rebel-held territory.

The OSCE's Michael Bociurkiw told a news conference on Friday: "Unfortunately the task was made very difficult. Upon arrival at the site ... we encountered armed personnel who acted in a very impolite and unprofessional manner. Some of them even looked slightly intoxicated." The gunmen claimed to have recovered both flight recorders from the aircraft.

Speaking at a press conference earlier on Friday in Berlin, Chancellor Angela Merkel called for an immediate halt to the fighting in eastern Ukraine.

"What is important now is for an independent investigation to take place as soon as possible," Merkel said. "For that, a ceasefire is needed, and then it is of course crucial for those responsible to be brought to justice."

Russia's UN Ambassador Vitaly Churkin called for an "impartial, open investigation of what happened." President Vladimir Putin said he was in contact with Ukraine's President Petro Poroshenko to achieve "long-term peace." Comments attributed to a pro-Russian rebel chief in Ukraine suggest the plane may have been shot down by mistake, by fighters believing it to be a Ukrainian army transport aircraft.

Ukraine has asked for assistance with an investigation from UN, US and European air safety organizations, the aircraft manufacturer Boeing, Malaysia and the Netherlands.

US President Barack Obama spoke with Chancellor Merkel, and the prime ministers of Britain and Australia on Friday to discuss how to respond to the downing of the aircraft. After Obama's conversation with Australia's Prime Minister Tony Abbott, the White House issued a statement saying: "The two leaders discussed the importance of a prompt, full, unimpeded and transparent international investigation, and they stressed the need for immediate access by international investigators to the crash site:"

Obama said the apparent shooting down of the plane was a "wake up call" for Europe particularly over the crisis in Ukraine.

jm/av (Reuters, AP, AFP)