The Wall Street Journal first reported the cause of the crash as a missile strike, citing unidentified U.S. intelligence sources. The sources did not specify which entity -- Ukraine, pro-Russian separatists, or Russia -- fired the missile.
An unnamed senior U.S. official told the Washington Post that U.S. intelligence agencies had confirmed the plane was downed by a surface-to-air missile and that analysts were working to determine the party responsible.
The Boeing 777, with 295 people aboard, crashed into Ukraine's restive eastern region, where pro-Russian armed separatists are battling Ukrainian armed forces for control of the area. "This is a contested area," the U.S. official told the Post. "It's going to take time to get some information on the intentions of whoever was involved."
President Barack Obama said Thursday, "The United States will offer any assistance we can to help determine what happened, and why." Biden later reported that an offer of assistance had been accepted by Ukrainian President Petro Poroshenko; a team of experts "will be on their way rapidly to see if we can get to the bottom of this."