KIEV, Ukraine (AP) -- A U.S. official says American intelligence authorities believe a surface-to-air missile took down a passenger jet carrying 298 people in eastern Ukraine on Thursday, but the Obama administration is still scrambling to confirm who launched the strike and whether there were American citizens killed in the crash.
Vice President Joe Biden says the incident was "not an accident," describing the Malaysia Airlines plane as having been "blown out of the sky."
Among the unanswered questions is whether the missile was launched from the Russian or Ukrainian side of the border they share. The official says U.S. intelligence assessments suggest it is more likely that pro-Russian separatists or Russians shot down the plane than Ukrainian forces.
The U.S. has sophisticated technologies that can detect missile launches, including the identification of heat from a rocket engine.
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). He also said it was hit by a missile fired from a Buk launcher, which can fire missiles up to an altitude of 22,000 meters (72,000 feet).
Ukraine's president says his country's armed forces did not shoot at any airborne targets, after reports that a Malaysian Airlines plane went down over Ukraine.
President Petro Poroshenko says Thursday "we do not exclude that this plane was shot down, and we stress that the Armed Forces of Ukraine did not take action against any airborne targets."
Poroshenko said "we are sure that those who are guilty in this tragedy will be held responsible."
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."
It was the second time that a Malaysia Airlines plane had gone missing in less than six months. Malaysia Airlines Flight 370 disappeared in March while en route from Kuala Lumpur to Beijing. It has not been found, but the search has been concentrated in the Indian Ocean far west of Australia.
The Donetsk region government said Thursday's plane crashed near a village called Grabovo, which it said is currently under the control of armed pro-Russian separatists. The region where the flight was lost has seen severe fighting between Ukrainian forces and pro-Russia separatist rebels in recent days.
A launcher similar to the Buk missile system was seen by Associated Press journalists near the eastern Ukrainian town of Snizhne earlier Thursday.
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.