The United States said on Wednesday that blame for the crashed Malaysian airliner lies directly with Russian President Vladimir Putin.

State Department spokeswoman Marie Harf told a regular briefing that Putin was responsible not just for the downing of the jetliner, "but every incident we've seen" throughout the conflict in Ukraine.

Russian separatists, who the United States strongly believes fired the missile that took down the plane, would not be there operating without the support of Putin and the Russian government, Harf said.

The spokeswoman added that investigators are still trying to figure out the motives of the culprits.

"We just don't know what their intentions are," Hard said, adding that the investigation will continue so "we could hold the people who did it accountable."

US intelligence officials on Tuesday told reporters that Russia was responsible for creating the conditions leading to the plane crash, but did not provide direct evidence of Moscow's involvement.

Harf also said that investigators are being given "better access" in Ukraine at the crash site, which is controlled by militants in eastern Ukraine.

The United States has urged Russia to ensure that the militants in eastern Ukraine allow free access to investigators and do not impede any probe.