1st LD-Writethru: Determining whether Americans on board downed plane first priority for U.S.: Obama

WASHINGTON, July 17 (Xinhua) -- U.S. President Barack Obama said on Thursday it is the "first priority" for the United States to determine whether any Americans were on board the downed passenger plane near the Ukraine-Russia border.

"The United States will offer any assistance we can to help determine what happened and why," he said, adding that the world is watching the event that "looks like might be a terrible tragedy. "

A Malaysian flight with 280 passengers and 15 crew members on board crashed in Ukraine near the Russian border, the Interfax news agency reported Thursday.

Obama and Russian President Vladimir Putin on Thursday talked about the reports of the downed jet, the White House said.

White House spokesman Josh Earnest told reporters that Obama and Putin spoke on Thursday morning at Moscow's request about the new sanctions against Russia and near the end of the call, the leaders noted the early reports about the plane crash.

Earnest said Obama had instructed his staff to keep him updated and to contact senior Ukrainian officials about the incident. But the spokesman said he is "not in a position to confirm" the plane crash.

State Department spokeswoman Jen Psaki told a press briefing on Thursday that the United States does not have any confirmed information about casualties, the cause or additional details concerning the incident.

"Our thoughts and prayers go out to those on board, their families and loved ones." Psaki said. "We're closely monitoring the situation."