The United States government has concluded that the passenger jet felled over Ukraine was shot down by a Russian-made surface-to-air missile launched from rebel-held territory and most likely provided by Russia to pro-Moscow separatists, according to a report by New York Times.

While American officials are still investigating the chain of events leading to the destruction of Malaysia Airlines Flight 17 last Thursday, they pointed to a series of indicators of Russian involvement. Among other things, military and intelligence officials said there was mounting evidence that a Ukrainian military plane shot down three days earlier had been fired upon from inside Russian territory by the same sort of missile battery used to bring down the civilian jet.

The intelligence persuaded President Obama to publicly lay responsibility at least indirectly at the door of the Kremlin. Speaking at the White House, he tried to channel international indignation toward Russia for what he called an “outrage of unspeakable proportions.” Mr. Obama said the episode should be “a wake-up call for Europe” and “should snap everybody’s heads to attention” about what is going on in Ukraine, where a pro-Russia insurgency has become an international crisis.

Without going into detail about the intelligence he had been shown, Mr. Obama said that the separatists had been armed and trained “because of Russian support.” High-flying aircraft cannot be shot down without sophisticated equipment and training, he added, “and that is coming from Russia.”

He singled out President Vladimir V. Putin of Russia, accusing him of waging a proxy war that led to the tragedy. “He has the most control over that situation,” Mr. Obama said, “and so far, at least, he has not exercised it.”

Russia denied involvement and suggested that Ukraine’s military might have been responsible, an assertion Ukraine rejected. Mr. Putin called for talks, saying: “All sides to the conflict must swiftly halt fighting and begin peace negotiations. It is with great concern and sadness that we are watching what is happening in eastern Ukraine. It’s awful; it’s a tragedy.”

As investigators tried to sort out control of the crash site in the middle of a war zone and families mourned the victims, the global revulsion at the downing of the plane grew, particularly with the news that a number of AIDS researchers were among the dead. European leaders joined Mr. Obama in calling for an international investigation unimpeded by combatants, and Ukraine asked the United Nations civil aviation authority to lead an investigation.

The president stated that an immediate cease-fire must take place in eastern Ukraine to allow for an international investigation into the Malaysian airline crash.

While separatists guarding the crash site allowed some Ukrainian government rescue teams to enter and begin collecting bodies on Friday, the Organization for Security and Cooperation in Europe said the armed rebels had prevented its monitors from gaining full access to the site in order to secure a safe route for the investigation and salvaging operations.

One rebel even fired into the air as the monitors were leaving, according to a spokesman for the organization, Michael Bociurkiw, who was there. Mr. Bociurkiw said bodies in the field were beginning to bloat. A separatist leader said that the governments of the Netherlands and Malaysia had asked the rebels informally not to disturb the crime scene, but that there were not enough refrigerators to keep the bodies there.

Among the 298 people who died when the plane came down was Quinn Lucas Schansman, 19, who was born in New York to a Dutch father and had dual American and Dutch citizenship. Mr. Schansman had been studying in Amsterdam when he decided to fly to Indonesia, where his family was on a three-week vacation. “He was headed over there to meet them,” said Katinka Wallace, a relative.

Mr. Schansman’s Facebook page indicated that he had moved to Amsterdam on April 24 and had been in a relationship with a young woman since last year. His favorite quotation was “I have a dream!” On Friday, friends and relatives posted remembrances in Dutch. “Dear cousin and friend, we’re going to miss you,” one wrote.