Obama On Malaysia Plane Crash: U.S. 'Will Offer Any Assistance We Can'

President Barack Obama spoke briefly on the Malaysia Airlines passenger jet that was shot down over Ukraine on Thursday, saying the United States "will offer any assistance we can to determine what happened and why."

"Looks like it may be a terrible tragedy. Right now we're working to determine whether there were American citizens on board, that is our first priority," Obama said.

Obama was briefed on reports of the plane shortly after news broke Thursday. He made his remarks before giving a speech on the economy while visiting Delaware.

UPDATE: 8:57 p.m. ET The number of people aboard the Malaysian Airlines plane that crashed over Ukraine has been updated to reflect the latest information from Malaysia Airlines.

Below, more on the crash from the AP:

KIEV, Ukraine (AP) A Ukrainian official said a passenger plane carrying 298 people was shot down Thursday over a town in the east of the country, and Malaysian Airlines tweeted that it lost contact with one of its flights over Ukrainian airspace.

Anton Gerashenko, an adviser to Ukraine's interior minister, said on his Facebook page the plane was flying at an altitude of 10,000 meters (33,000 feet) when it was hit by a missile fired from a Buk launcher. A similar launcher was seen by Associated Press journalists near the eastern Ukrainian town of Snizhne earlier Thursday. The Buk missile system can fire missiles up to an altitude of 22,000 meters (72,000 feet).

Malaysia Airlines said on its Twitter feed that it "has lost contact of MH17 from Amsterdam. The last known position was over Ukrainian airspace. More details to follow."

The region has seen severe fighting between Ukrainian forces and pro-Russia separatist rebels in recent days.

On Wednesday evening, a Ukrainian fighter jet was shot down by an air-to-air missile from a Russian plane, Ukrainian authorities said Thursday, adding to what Kiev says is mounting evidence that Moscow is directly supporting the separatist insurgents in eastern Ukraine. Security Council spokesman Andrei Lysenko said the pilot of the Sukhoi-25 jet hit by the air-to-air missile was forced to bail after his jet was shot down.

Pro-Russia rebels, meanwhile, claimed responsibility for strikes Wednesday on two Ukrainian Sukhoi-25 jets. The Ukrainian Defense Ministry said the second jet was hit by a portable surface-to-air missile, but added the pilot was unscathed and managed to land his plane safely

Moscow denies Western charges that is supporting the separatists or sowing unrest in its neighbor. The Russian Defense Ministry couldn't be reached for comment Thursday about the Ukrainian jet and Russia's foreign ministry didn't respond to multiple requests for comment.

Earlier this week, Ukraine said a military transport plane was shot down Monday by a missile fired from Russian territory.

The rebels are known to possess portable anti-aircraft rocket launchers, but Ukrainian officials say that kind of weapon would have been unable to reach Monday's plane at the altitude at which it was flying Monday. Aviation experts, however, have questioned whether the stricken transport plane was flying at the altitude Ukrainian officials had claimed.

See updates on the situation below: