"The world is watching reports of a downed passenger jet near the Russia-Ukraine border, and it looks like it may be a terrible tragedy," Obama said at Wilmington in Delaware, where he delivered remarks on the US infrastructure.
"Right now we're working to determine whether there were American citizens on board. That is our first priority. I've directed my national security team to stay in close contact with the Ukrainian government," he said.
Earlier the US President was informed about the plane crash by Russian President Vladimir Putin, a presidential spokesman said.
Earlier he was briefed by his national security team on the accident.
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The United States is closely monitoring the situation, State Department Spokesperson Jen Psaki said.
"At this point, we do not have any confirmed information about casualties, the cause or additional details. Our thoughts and prayers go out to those on board, their families and loved ones," she told reporters at her daily news conference.