Washington/New York: The United States believes a surface-to-air missile brought down the Malaysian airliner that crashed on Thursday in eastern Ukraine, killing all 298 people aboard, two US officials said.
One US official, speaking on condition of anonymity, said the origin of the missile was unclear. The official declined further comment.
But a second official said Washington strongly suspected the missile was fired by Ukrainian separatists backed by Moscow. There is no evidence that Ukrainian government forces fired a missile or have any missile systems missing, the second official said.
Ukraine accused "terrorists" - militants fighting to unite eastern Ukraine with Russia - of shooting down the Malaysia Airlines Boeing 777 with a heavy Soviet-era SA-11 ground-to-air missile as the plane flew from Amsterdam to Kuala Lumpur. Leaders of the rebel Donetsk People's Republic denied any involvement.
US 'horrified' by Ukraine plane crash: Kerry
US Secretary of State John Kerry called Thursday for a "credible" international investigation into the apparent downing of a Malaysian airliner over rebel-held eastern Ukraine, expressing horror at the incident.
"We are horrified by the crash of Malaysia Airlines flight MH17," Kerry said in a statement. "The United States government remains prepared to assist with a credible, international investigation any way we can, and we will continue to be in touch with all relevant partners as we seek the facts of what happened today."
Barack Obama pledges US help for Malaysian plane probe
President Barack Obama directed US officials on Thursday to do all they could to support an investigation into what caused a Malaysian jetliner to crash in a Ukrainian war zone and pledged support to the affected countries as the probe moves forward.
Obama went ahead with a trip to tout infrastructure investment in Delaware and to raise money for Democrats in New York despite the incident in which more than 290 people were killed. A Ukrainian official said there were 23 Americans aboard but US officials did not confirm that.
Before leaving the White House, Obama spoke by telephone to Russian President Vladimir Putin after the United States on Wednesday imposed the most wide-ranging sanctions yet on Moscow for its actions in Ukraine. During the call, which came at Russia's request, Putin informed Obama about the downed plane.
“I can confirm that President Putin near the end of this morning's phone call with President Obama noted the early reports of a downed passenger jet near the Russia-Ukraine border," White House spokesman Josh Earnest said.
Ukraine and Russia traded accusations of blame over the incident.
Obama made brief remarks about the plane at the beginning of a speech about roads and bridges in Wilmington, Delaware.
"It looks like it may be a terrible tragedy," he said. "I’ve directed my national security team to stay in close contact with the Ukrainian government. The United States will offer any assistance we can to help determine what happened and why."
Vice President Joe Biden said it appeared the downing of the jetliner near the Ukraine-Russia border was not an accident and that the passenger jet apparently was "blown out of the sky."
"This is truly a grave situation," he said during a speech in Detroit.
Both Obama and Biden spoke by phone with Ukrainian President Petro Poroshenko, offering assistance to help determine what happened to the Boeing 777 that was flying from Amsterdam to Kuala Lumpur, officials said.
Obama and his Ukrainian counterpart emphasized that evidence from the crash must remain in Ukraine so international investigators have a chance to look at all of it, officials said.
Obama also called Malaysian Prime Minister Najib Razak and Dutch Prime Minister Mark Rutte to express condolences and offer US support for a full probe. The White House said Obama told Rutte that the United States "was prepared to contribute immediate assistance to support a prompt, full, credible and unimpeded international investigation."
Adds unpredictable element
The crash injected an unpredictable element into the increasingly violent confrontation between Ukraine and Russian-backed separatists in eastern Ukraine.
Republican lawmakers, who have called for tough US action against Moscow over Ukraine, called for retaliation against Russia if it were found to have been involved in the crash.
"I believe there should be serious consequences if we find out that it was either Russian agents, Russian equipment or Russians directly that was responsible for the downing of this airliner," New Hampshire Republican Senator Kelly Ayotte said in a speech in the US Senate.
Obama, determined not to appear to be a hostage of world events, continued with his trip after telling Putin that the United States could impose more sanctions on Russia if Moscow does not take steps to de-escalate the Ukraine crisis.
The new round of US sanctions against Russia included penalties against Russia's largest oil producer, Rosneft, and other energy, financial and defense firms.
In Wilmington, Obama ate a hamburger with a supporter at a diner after shaking hands and hugging children in the restaurant. In New York, he attended Democratic fundraisers that were not open to the press.
Seeking to show that Obama was on top of the crisis despite his travel, the White House said he convened separate calls with Secretary of State John Kerry and senior members of his national security team, including CIA Director John Brennan, after Air Force One arrived in New York.