President Obama said Friday that the missile that downed a Malaysian airliner, killing 298 people aboard, was fired from territory controlled by pro-Russia separatists.
"What we have confidence in saying ... a surface-to-air missile was fired, and that's what brought the jet down. That shot was taken in a territory controlled by the Russian separatists," Obama said in remarks made at the White House.
He called for an immediate cease-fire in the war-torn region of eastern Ukraine where the plane was shot down Thursday.
"My concern is there has been a lot of misinformation generated in eastern Ukraine generally. This should snap everybody's heads to attention," Obama said. "We need to know exactly what happened."
A U.S. official earlier had told the Los Angeles Times that U.S. intelligence agencies reached a preliminary conclusion that pro-Russia separatists in Ukraine fired the missile that brought down a Malaysian airliner.
The U.S. is seeking further intelligence before reaching a final conclusion, the official said.
The agencies are also examining to what extent the Russian government may have been involved in the incident, but have reached no conclusions, the official said.
Even the initial finding that pro-Russia forces were involved will intensify international pressure on Moscow, which backs the separatist groups in eastern Ukraine. It could force Obama and U.S. allies in Europe to respond with new steps only days after they imposed new sanctions on Russian financial institutions, energy companies and arms firms in response to Moscow's intervention in Ukraine.
The plane was traveling from Amsterdam to Kuala Lumpur, Malaysia, on a route that took the aircraft over the eastern Ukraine where attacks on military aircraft by Russian-backed separatists have increased in recent weeks.
A prominent AIDS researcher and others en route to the 20th International AIDS Conference in Melbourne, Australia, were among the victims. More than half of those on the plane were from the Netherlands, officials said. Dozens of Australians and Malaysians also were on the plane, officials said.
Russia has denied any involvement in the downing of the aircraft.
Sergei Kavtaradze, a member of the Security Council of the self-proclaimed Donetsk People's Republic, also told The Times on Thursday that it "was not us who shot down the plane because we don't have this hardware." Kavtaradze was referring to a Buk missile system, which can propel missiles high into the air at great speed.
Malaysian officials on Friday defended the decision to fly over the troubled region. The Malaysian transportation minister said he believed the crew bore no responsibility for the flight plan.
"The flight path taken by MH17 was approved by the International Civil Aviation Organization and by the countries whose airspace the route passed through," said Liow Tiong Lai at a news conference in Kuala Lumpur. "Fifteen out of 16 airlines in the Assn. of Asia Pacific Airlines fly this route over Ukraine."
Wreckage from the crash was spread over a wide area in the contested territory around Donetsk.
Within hours of Thursday's crash, flight radar showed a clear pattern of aircraft avoiding Ukraine. U.S. officials late Thursday extended a ban on American aircraft entering airspace in that region, although Federal Aviation Administration officials noted that U.S.-based commercial carriers already had no regular flight routes in the problem areas.
President Obama addressed the crash at noon EDT from the White House.