The United States said on Saturday it is "deeply concerned" by rebels' refusal to allow monitors safe and unfettered access to the crash site of the doomed Malaysia airliner.

"The site is not secure, and there are multiple reports of bodies being removed, parts of the plane and other debris being hauled away, and potential evidence tampered with," State Department spokeswoman Jen Psaki said in a statement.

She added thus far, the separatists in eastern Ukraine have only allowed monitors to have limited access to a small area.

"This is unacceptable and an affront to all those who lost loved ones and to the dignity the victims deserve," the spokeswoman said.

Malaysian Airline MH17 with 298 people on board was shot down Thursday in Ukraine near the Russian border when it was en route from Amsterdam to Kuala Lumpur. No survivors have been found from the crashed plane.

Psaki called for "a full, credible, and unimpeded international investigation as quickly as possible", noting that both rebels and Russia had committed to allowing full access to international observers and response teams.

The United States urges Russia to honor its commitments and to publicly call on the separatists to do the same, she added.