Data downloaded from a black box retrieved from the wreckage of Malaysia Airlines Flight 17 are consistent with a missile attack, national news media are reporting, citing an unidentified European air safety official.
The source told CBS News the findings indicate the plane's fuselage was hit by shrapnel from a missile explosion.
"It did what it was designed to do — bring down airplanes," the source told CBS.
A thorough investigation of the site, however, remains elusive 10 days after the jetliner crashed in an area of eastern Ukraine held by ethnic-Russian separatists. On Sunday, a team of international police officers cleared by separatist leader Alexander Borodai to visit the site canceled the trip when fighting broke out in the area.
Alexander Hug, the deputy head of a monitoring team from the Organization for Security and Cooperation in Europe, said it was too dangerous for the unarmed officers to travel to the site.
Hug said the police mission, which is comprised of officers from the Netherlands and Australia, will reconsider resuming operations if security improves. Australian prime minister Tony Abbott had said earlier Sunday that unarmed Australian police would be sent to the crash site as part of a Dutch-led police force to secure the area and help recover victims' remains. Crash victims include 37 Australians.
Ukraine's National Security Council said that government troops have encircled Horlivka, a key rebel stronghold near the crash site. A representative of the separatist military command in Donetsk confirmed that there had been fighting in Horlivka, but said that rebel fighters were holding their positions.
The Amsterdam-to-Kuala Lumpur flight crashed July 17, killing all 298 people on board, most of them Dutch citizens. U.S. and Ukrainian officials say it was shot down by a missile from rebel territory, most likely by mistake.
Ukrainian foreign minister Pavlo Klimkin, speaking Sunday on CBS' Face the Nation,that Russia was responsible for the air tragedy. He acknowledged that separatists could easily buy some weapons on the black market, but that there are limits.
"How can you buy on the black market a highly sophisticated, anti-aircraft missile capable to shoot down planes at the altitude of 10,000 meters?" Klimkin said. "You imagine that the terrorists can operate highly sophisticated weapons there? It's of course about responsibility of those (Russians) who bring also across the border all inflow of weapons and weaponry.''
Russian Deputy Defense Minister Anatoly Antonov has repeatedly dismissed accusations that ethnic-Russian separatists — or Russians themselves — shot down the plane, saying that if the U.S. officials had proof "how come they have not been made public?"
On Saturday, the parents of a 25-year-old victim visited the site. Angela Rudhart-Dyczynski and Jerzy Dyczynski traveled from Perth, Australia, and had to cross dangerous pro-Russian rebel-held territory to honor their daughter, Fatima.
"We have promised our daughter we will come here," Rudhart-Dyczynski told NBC News.
Flights from Ukraine to the Netherlands have taken 227 caskets containing victims of the plane disaster. Officials say the exact number of people held in the caskets still needs to be determined by forensic experts in the Netherlands.
Ukraine's National Security Council spokesman Andrei Lysenko said that Ukrainian troops were engaging rebels in fighting at several locations Sunday, including near the town of Debaltseve, which is 15 miles northwest of the crash site.
The Malaysia Airlines disaster prompted some expectation in the West that Russia would scale back its involvement in the uprising in Ukraine's east. However, Russia launched artillery attacks from its soil into Ukraine on Friday, while the United States said it has seen powerful rocket systems moving closer to the Ukraine border.
Contributing: Natalie DiBlasio and Martha T. Moore, USA TODAY; Associated Press