FBI, NTSB Investigators Headed to Site of Downed Malaysia Airlines Plane

People lay flowers and light candles in front of the Embassy of the Netherlands in Kiev on July 17, 2014, to commemorate passengers of Malaysian Airlines flight MH17 from Amsterdam to Kuala Lumpur which crashed in eastern Ukraine.The pro-Russian separatists who control the area where a Malaysia Airlines flight was brought down agreed today to allow investigators safe access to the site to recover bodies and gather evidence, according to a statement from the Organization for Security and Co-operation in Europe.

It was unclear how soon investigators would begin sifting through the charred wreckage of the airliner, which was carrying 298 people when it went down Thursday in Ukraine near the Russian border. The plane had left Amsterdam at 12:15 p.m. (local time) and was estimated to arrive in Kuala Lumpur International Airport on Friday at 6:10 a.m. (local time), according to Malaysia Airlines.

FBI and NTSB officials will head to Ukraine in an "advisory role" in the investigation, a senior administration official told ABC News.

John Wendle, a freelance reporter for ABC News, described seeing "bodies scattered everywhere" at the crash site.

"There's blood splattered everywhere, and pieces of remains," Wendle said. "It's a pretty grim sight...This is terrible."

A U.S. official told ABC News intelligence and analysis of the situation determined that it was a single surface-to-air 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 added.

Men stand next to the wreckage of the Malaysian airliner that crashed near the town of Shaktarsk in rebel-held east Ukraine on July 17, 2014.It remains unclear if Americans were on board the flight. Malaysia Airlines officials said that 154 passengers were Dutch. In addition, according to the latest numbers released by the airline, 43 were Malaysian, 27 Australians, 12 Indonesians, 9 British, 4 Belgians, 4 Germans, 3 Filipinos and 1 Canadian. Nationalities of 41 other passengers remain unknown at this time.

The International AIDS Society said in a statement it was looking into reports that some of its members may have been on the flight en route to the International AIDS Conference taking place in Melbourne, Australia.

"At this incredibly sad and sensitive time the IAS stands with our international family and sends condolences to the loved ones of those who have been lost to this tragedy," the statement reads.

The White House issued a statement calling it "vital that no evidence be tampered with in any way and that all potential evidence and remains at the crash site are undisturbed" until an investigation can begin.

"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," the statement said.

The family member of a passenger killed in the crash of Air Malaysia flight MH17 grieves as he waits on a bus to depart Schiphol airport in Amsterdam, Netherlands."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," the White House statement said. "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."

Investigators will also be tasked with determining the series of events leading up to the crash.

Ukrainian authorities told U.S. Embassy officials that debris was spread out over a 10-mile path near the town of Hrabove in the Donetsk region of eastern Ukraine.

A statement from the Foreign Ministry in Kiev claimed the plane had been "shot down."

"According to the General Staff of Ukrainian Armed Forces, the airplane was shot down by the Russian Buk missile system as the liner was flying at an altitude of 10,000 meters [33,000 feet]," the statement reads. "Ukraine has no long-range air defense missile systems in this area. The plane was shot down, because the Russian air defense systems was affording protection to Russian mercenaries and terrorists in this area. Ukraine will present the evidence of Russian military involvement into the Boeing crash."

Ukrainian President Petro Poroshenko later added, "We are not calling it an accident, or a disaster, but an act of terrorism."

In a tweet soon after the plane went down, Russian President Vladimir Putin said, "Condolences to Malaysian Prime Minister Najib Razak in connection with the crash of a passenger aircraft in Ukraine."

A Kremlin statement said Putin opened a meeting with his economic advisers by calling for a moment of silence over the crash.

"This tragedy would not have happened if there were peace on this land, if the military actions had not been renewed in southeast Ukraine," he said. "And, certainly, the state over whose territory this occurred bears responsibility for this awful tragedy."

The plane did not make a distress call and the route had been deemed safe by the International Civil Aviation Organization despite the ongoing fighting in Ukraine, Malaysia's Prime Minister Najib Razak said.

The FAA on Thursday issued an order that U.S. flight operations avoid airspace over eastern Ukraine, expanding on a previous warning about flying over the contested Crimean region and additional portions adjacent to the Black Sea and the Sea of Azov.

At Schiphol Airport in Amsterdam, grieving family members gathered as airline officials briefed them. Malaysia Airlines said a manifest of the passengers would not be released until all next of kin were notified.

This is the second Malaysia Airlines plane to be involved in an air tragedy this year. On March 8, Malaysia Airlines Flight MH370 vanished with 239 people on board after it took off from Kuala Lampur bound for Beijing. Malaysian officials said the plane disappeared somewhere in the Southern Indian Ocean, but no wreckage has ever been recovered.