Malaysia Airlines flight MH17 was shot down over eastern Ukraine today—the plane's 283 passengers and 15 crew members are all presumed dead. The White House confirmed this afternoon that the Boeing 777 flying from Amsterdam to Kuala Lumpur was shot down by an antiaircraft missile, though it continues to be disputed who might be responsible.

Vice President Joe Biden told Ukrainian President Petro Poroshenko that the U.S. would be sending a team to aid in investigations, saying that the attack was "not an accident" and that the plane was "blown out of the sky." Poroshenko has described the shooting down of the plane an act of terrorism.

Ukraine and pro-Russian separatists, embroiled in a series of attacks, have blamed each other for shooting down the plane. Both are tossing around unconfirmed claims, accusations, and evidence: A supposed radio transmission between pro-Russian militants has surfaced in which they describe shooting the plane down by accident; some Russian news agencies are reporting that the missile attack was a botched assassination attempt on Vladimir Putin, who was apparently flying in the same region at the time of the attack.

Putin, meanwhile, rest the blame for the attack on Ukraine in comments he made in a televised conference.

"Certainly, the state over whose territory this happened bears responsibility for this terrible tragedy," Putin said. "This tragedy would not have happened if there was peace in this land, they would not have been renewed war-like actions in the southeast of Ukraine."

Should Russia or the separatists the country is supporting in Ukraine prove to have been behind the attack, it would echo a previous attack on a commercial airline flight from 30 years ago, when the Russian military shot down Korea Airlines Flight 007, killing its 269 passengers.

Journalists at the crash site have described a grisly scene, with body parts strewn across the Ukrainian wheat field where the plane went down. While the White House is still working to determine if any of the passengers were American, CNN reports that Dutch citizens made up a large portion of the flight.

"It looks like it might be a terrible tragedy," President Obama said today from Delaware. "Right now we're working to determine whether there were American citizens on board. That is our first priority."

The pro-Russian separatists, Reuters reports, have agreed to a temporary cease-fire to allow crews to clean up and work the crash site.

Update, 8:00 p.m.: Former Secretary of State Hillary Clinton told Charlie Rose today that while it continues to be unconfirmed who's responsible for the attack, there is apparently "growing awareness that it probably had to be Russian insurgents."

Update, 8:20 p.m.: Joep Lange, president of the International AIDS Society and a prominent AIDS/HIV researcher, has been confirmed among the dead. Lange was travelling amongst a group of researchers on their way to the AIDS 2014 conference in Melbourne. The Guardian reports that up to 100 people on the plane were en route to the conference.

Update, 8:26 p.m.: Malaysia Airlines has upped the death toll to 298 to include three infants that also died in the crash. From their statement:

As opposed to the earlier statement, the flight was carrying a total number of 298 people – comprising 283 passengers including three infants of various nationalities and 15 crew of Malaysian nationality. Some of the nationalities of the passengers are yet to be determined.

Update, 9:52 p.m.: The FAA has banned all American flight operations over eastern Ukraine until further notice.

Update, 10:22 p.m.: According to the New York Times, wreckage from the plane covers six square miles.

Update, 11:30 p.m.: The White House has expressed concern that crucial evidence at the crash site might be tampered with. From their statement:

The United States is shocked by the downing of Malaysian Airlines Flight 17, and we offer our deep condolences to all those who lost loved ones on board. We continue to seek information to determine whether there were any American citizens on board.

It is critical that there be a full, credible, and unimpeded international investigation as quickly as possible. We urge all concerned – Russia, the pro-Russian separatists, and Ukraine – to support an immediate cease-fire in order to ensure safe and unfettered access to the crash site for international investigators and in order to facilitate the recovery of remains. The role of international organizations – such as the United Nations and the OSCE in Ukraine – may be particularly relevant for this effort, and we will be in touch with affected nations and our partners in these organizations in the coming hours and days to determine the best path forward. In the meantime, it is vital that no evidence be tampered with in any way and that all potential evidence and remains at the crash site are undisturbed. The United States remains prepared to contribute immediate assistance to any international investigation, including through resources provided by the NTSB and the FBI.

While we do not yet have all the facts, we do know that this incident occurred in the context of a crisis in Ukraine that is fueled by Russian support for the separatists, including through arms, materiel, and training. This incident only highlights the urgency with which we continue to urge Russia to immediately take concrete steps to de-escalate the situation in Ukraine and to support a sustainable cease-fire and path toward peace that the Ukrainian government has consistently put forward.

[Image via AP]