US ambassador to the UN Samantha Power has said investigators of the Malaysia Airlines MH17 plane crash "cannot rule out technical assistance from the Russian personnel."

Power made the comment during an emergency meeting of the United Nations Security Council in New York.

She said the US supsects pro-Russia separatists in eastern Ukraine are responsible for having shot down with a SA-11 surface-to-air missile the aircraft on Friday.

All the 298 passengers, including 80 children, are believed to have died in the accident.

"Because of the technical complexity of the SA-11, it is unlikely that the separatists could effectively operate the system without assistance from knowledgeable personnel," she said. "Thus, we cannot rule out technical assistance from Russian personnel in operating the systems."

A few moment before news of the plane crash broke on Thursday afternoon, the separatists claimed on social media they had shot down a military aircraft.

"Separatists claimed responsibility and posted videos that are now being connected to the Malaysian Airlines crash," Power explained. "Separatist leaders also boasted on social media about shooting down a plane, but later deleted these messages.

"If indeed Russian-backed separatists were behind this attack on a civilian airliner, they and their backers would have good reason to cover up evidence of their crime. Thus it is extremely important than an investigation be commenced immediately."

Power said Ukraine also has SA-11 missiles but the US is not aware of any in the area where the plane was shot down.