A Malaysian airliner was shot down over eastern Ukraine on Thursday, killing nearly 300 people aboard, according to USA Today.

The airliner, en route from Amsterdam to Kuala Lumpur, disappeared from radar at 33,000 feet, and then crashed near the city of Shakhtarsk in Ukraine's Donetsk region, according to the International Business Times.

Malaysia Airlines said on its Twitter feed that it lost contact with Flight MH17 from Amsterdam to Kuala Lumpur at 2 p.m. GMT.

The Donetsky region is a stronghold of pro-Russian rebels. According to reports, pro-Russian rebels were the first to arrive at the site and take control.

An Associated Press journalist had counted "at least 22 bodies" at the site of smoldering debris and body parts.

Ukrainian President Petro Poroshenko called the downing an act of terrorism and called for an international investigation into the crash.

Malaysian Prime Minister Najib Razak says he is launching an immediate probe into the crash.

The Ukrainian military and pro-Russian rebels have accused each other of shooting down the plane, and both sides say they were not responsible.

"Flight recorders have been found at the crash site, Konstantin Knyrik, a spokesman for the pro-Russian rebels, has told Interfax news agency. Earlier reports quoted rebels as saying they intended to send the flight recorders to Moscow for checking," the BBC reported.

ABC News reported that a U.S. official said the U.S. believes a surface-to-air missile brought down the Malaysian Airlines jet: "The official said U.S. intelligence and analysis of the situation determined that it was a single missile that struck the Boeing 777-200 aircraft while at cruising altitude. It is unclear whether the missile was fired from inside Ukrainian or Russian territory and who fired it." The official said "he missile was not a shoulder-fired missile, but a larger complex surface to air missile system," ABC News reporter Jonathan Karl tweeted.

Several airlines, including Air France, British Airways, Italy's Alitalia, Lufthansa, Russia's Aeroflot and Turkish Airlines, say they will avoid eastern Ukrainian airspace in the wake of the incident. Eurocontrol said Ukrainian airspace "has now been closed," according to BBC News.

On the plane manifest were 23 U.S. citizens, Fox News reported, although the U.S. State Department wouldn't confirm that, and 40 children, according to The Independent.

The Kremlin website published a statement saying President Barack Obama was on Air Force One talking to Russian President Vladimir V. Putin when news of the crash was announced.

"A terrible tragedy," Obama told reporters at an event Wilmington, Delaware. He said his first priority would be to determine if U.S. citizens were onboard and offer any assistance to help determine what happened. "Our thoughts and prayers are with all the families of the passengers, wherever they call home," he added.

The New York Times reported that the Obama administration had "imposed a new round of sanctions against Russia on Wednesday," targeting the financial, energy and defense industries. Obama has said the sanctions will be lifted when Moscow halts "the flow of fighters and weapons across the border with Ukraine," supports a cease-fire and helps release hostages held by pro-Russian forces. Russia denounced the new sanctions, The Times reported.

For four months Ukraine has been the center of a conflict between Ukrainian troops and pro-Russian rebels. "Russia annexed the southern Crimean peninsula from Ukraine in March and has been accused of arming the rebels and even sending regular Russian soldiers to the eastern regions of Donetsk and Luhansk," a claim denied by Moscow, the BBC reported.

"More than 1,000 civilians and combatants have been killed since mid-April, when Ukrainian security forces moved to regain control of the eastern regions, while tens of thousands of people have left the region," the BBC added.