Investigators seek answers in MH17 crash as accusations, blame fly

(CNN) -- Hours after a Malaysia Airlines jet fell from the sky in eastern Ukraine with 298 people aboard, Russia and Ukraine traded blame and accusations.

Ukraine accused "terrorists" of downing the jet Thursday, using a word it routinely applies to describe pro-Russian separatists.

"Terrorists have killed almost 300 persons with one shot," Ukrainian President Petro Poroshenko said. "Among them are women, children, citizens of different countries of the world."

Russian President Vladmir Putin pointed the finger back at Ukraine, blaming its recent tough military operations against separatists for the volatility in the region.

Caught up in a foreign conflict

If the pro-Russian separatists did shoot down Malaysia Airlines Flight 17, the jet's passengers and crew are innocent casualties in Ukraine's separatist armed crisis.

The passengers and crew hailed from all over the world, including Australia, Indonesia, Malaysia, Germany and Canada. Shortly after the plane fell from the sky, international leaders scrambled to confirm how many of their citizens were aboard. The United States has not said whether its citizens were among passengers aboard, but the diversity of the victims' nationalities turned the crash into a global tragedy.

International inspectors headed to the crash site Friday to search for the flight data recorders among human remains and debris.

A helicopter ferried a group of monitors from the Organization for Security and Cooperation in Europe to rebel territory in the Donetsk region. They plan to continue by car to the crash site near Torez.

"We may be the first international group allowed to go through rebel territory to the site," said Michael Bociurkiw, who was traveling with about 30 colleagues.

'Blown out of the sky'

U.S. Vice President Joe Biden said Ukraine's President had accepted an offer of U.S. experts to help investigate the crash.

The plane was apparently shot down,"not an accident, blown out of the sky," Biden said Thursday.

Leaders and diplomats from around the world are pleading for investigators' access.

"It is critical that there be a full, credible, and unimpeded international investigation as quickly as possible," the White House said in a statement.

Radar system provides details

The United States has concluded that a missile shot down the plane, but has not placed any blame, a senior U.S. official said.

A radar system saw a surface-to-air missile system turn on and track an aircraft right before the plane went down, the senior U.S. official said. A second system saw a heat signature at the time the airliner was hit, the official said. The United States is analyzing the trajectory of the missile to try to learn where the attack came from, the official said.

The Obama administration believes Ukraine did not have the capability in the region -- let alone the motivation -- to shoot down the plane, a U.S. official told CNN's Jake Tapper.

But the White House placed some blame on Russia and warned that evidence must not be tampered with.

"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," it said in a statement.

But defense expert and retired Brig. Gen. Kevin Ryan said Ukraine and Russia both have the missile capability to shoot down such an aircraft for such an altitude.

The 15 crew members on Malaysia Airlines Flight 17 were all Malaysian nationals, officials said.

Malaysia Airlines also gave a breakdown of the known nationalities of the 283 passengers: 154 were Dutch, 28 were Australians, 28 were Malaysians, 12 were Indonesian, nine were from the United Kingdom, four were from Germany; four were from Belgium, three were from the Philippines, one was Canadian and one was from Hong Kong.

Authorities were still trying to determine the nationalities of the other passengers.

The International AIDS Society said in a statement that "a number" of its members were on the plane on the way to attend a conference 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 said.

Russia-Ukraine dispute

The plane was headed to the Malaysian capital of Kuala Lumpur from Amsterdam, which is a common route, CNN aviation safety consultant Mary Schiavo said. She said that the plane was flying over a troubled area and that close communication with air traffic controllers would be a key necessity.

Torez is in a rebel-held area.

In hostile or disputed areas, "any alteration from your course, and you can have a problem," Schiavo said.

Tensions have been high between Ukraine and Russia since street protests forced former pro-Moscow President Viktor Yanukovych from power in February. Russia subsequently annexed Ukraine's southeastern Crimea region, and a pro-Russian separatist rebellion has been raging in Ukraine's eastern Luhansk and Donetsk regions.

Ukrainian forces have been struggling to quell the separatist unrest. Ukraine's government has accused Russia of allowing weapons and military equipment, including tanks, to cross the border illegally into the hands of pro-Russian separatists.

Three months ago, the U.S. Federal Aviation Administration prohibited U.S. airlines from flying in areas not far from where Flight 17 reportedly crashed Thursday. "Due to the potential for conflicting air traffic control instructions from Ukrainian and Russian authorities and for the related potential misidentification of civil aircraft, United States flight operations are prohibited until further notice in the airspace over Crimea, the Black Sea and the Sea of Azov," the FAA said in April. Thursday's plane crash reportedly was in eastern Ukraine, scores of miles north-northeast of the Sea of Azov.

Various nations, including France, ordered their airlines to avoid Ukrainian airspace until the cause of crash is known.

Airline's troubles

Thursday's crash marks the second time this year that Malaysia Airlines has faced an incident involving a downed plane.

On March 8, Malaysia Airlines Flight 370 disappeared with 239 people on board. Searchers have found no trace of the Boeing 777 or its passengers despite extensive search efforts.

Flight 370 probably flew into the southern Indian Ocean on autopilot with an unresponsive crew, Australian authorities said last month.

During the early phase of the search for Flight 370, aircraft and ships scoured vast stretches of the surface of the southern Indian Ocean but found no debris.

Pings initially thought to be from the missing plane's flight recorders led to a concentrated underwater search that turned up nothing.

A new underwater search is expected to begin farther south in August. It will be broadly in an area where planes and vessels had already looked for debris on the surface of the water.