(CNN) -

A Malaysia Airlines passenger jet crashed in a rebel-controlled part of eastern Ukraine on Thursday, spurring swift accusations from Ukrainian officials that "terrorists" shot down the aircraft.

The United States has concluded a missile shot down the plane, but hasn't pinpointed who was responsible, a senior U.S. official told CNN's Barbara Starr.

The Boeing 777 with 298 people aboard fell from the sky near the town of Torez in the Donetsk region of eastern Ukraine, officials said. A top Ukrainian official said the plane, which was on the way from Amsterdam to Kuala Lumpur, was flying at about 10,000 meters (nearly 33,000 feet) when the missile hit.

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.

Malaysian Prime Minister Najib Razak said the plane never made a distress call.

He called for an international team to have full access to the crash site.

"We must and we will find out precisely what happened to this flight. No stone will be left unturned," he said.

"If it transpires that the plane was indeed shot down, we insist that the perpetrators must swiftly be brought to justice," Najib said.

Ukrainian officials maintained that pro-Russian separatists were behind the crash.

Russian President Vladimir Putin said Ukraine's military campaign against the separatists was to blame.

"This tragedy would not have happened, if there had been peace on that land, or in any case, if military operations in southeastern Ukraine had not been renewed," Putin said in televised remarks. "And without a doubt the government of the territory on which it happened bears responsibility for this frightening tragedy."

Ukraine's state security chief accused two Russian military intelligence officers of involvement and said they must be punished.

Valentyn Nalyvaichenko said he based his allegation on intercepts of phone conversations between the two officers. "Now you know who carried out this crime. We will do everything for the Russian military who carried out this crime to be punished," he told reporters.

The jet plunged toward the ground in a fireball, leaving a trail of black smoke behind in the sky.

Emergency crews scrambled to what witnesses described as a staggering scene of death and utter destruction.

"People said the plane kind of exploded in the air, and that everything rained down in bits and pieces, the plane itself, the people inside," said Noah Sneider, an American freelance journalist who interviewed witnesses at the scene.

Charred wreckage stretched for kilometers, he said. Stunned rescue workers and rebel fighters combed the area, Sneider said, planting sticks with white cotton ribbons where they found bodies in the fields.

"As you walk through the fields, you see a man with his cracked iPhone sticking out of his pocket. You see sort of people's clothing everywhere. Most of it's kind of ripped off by the air. There's some suitcases and stuff in a pile by the road," Sneider said.

There were many bodies left to be found as night fell, he said, and people were trying to figure out what to do next.