US intelligence officials said they believe pro-Russian separatists in eastern Ukraine probably shot down MH17 "by mistake".
However, the US admitted not knowing exactly who fired the surface-to-air missile that downed the Malaysian Airlines plane.
Russia is continuing to deliver more weapons, including rockets and tanks, to separatists, officials added.
The intelligence officials also said the US did not know separatists had Russian SA-11 missiles until after the plane was hit.
Thousands of online users have taken to social media to call for the victims of the Malaysian airliner crash to be returned to loved ones.
United States intelligence officials admitted that they do not know who fired the surface-to-air missile that downed flight MH17.
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