Who shot down MH17?

Ukraine

President Petro Poroshenko's spokesman said he believed pro-Russian insurgents downed the jet.

Prime Minister Arseniy Yatsenyuk said Friday that pro-Russian separatist rebels should face an international tribunal in The Hague.

Russia

President Vladimir Putin said Kiev bore full responsibility for the crash, saying Ukraine's crackdown on separatist rebels stoked tensions that led to the disaster.

The Russian defense ministry said Friday that a Ukrainian radar station of the Buk-M1 system located near the south of Donetsk was operating on the day MH17 was downed.

US

"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, material, and training," the White House said in a statement.

A classified US intelligence analysis said it is most likely that pro-Russian separatists fired the missile that downed MH17, CNN reported.

Rebels

A spokesman for the rebels in Donetsk, Sergei Kavtaradze, said that "according to our information this plane was shot down by Ukrainian armed forces."

AFP said social media posts by pro-Russian insurgents - most of them hastily removed - suggest the rebels thought they had shot down a Ukrainian army plane before realizing in horror that it was in fact a passenger plane.

Do the rebels have a sophisticated enough surface-to-air missile system to strike the passenger jet?

Rebel leaders were quoted in Russian paper Izvestia as saying the rebels who control the area of the crash had no weaponry as sophisticated as the Buk, a surface-to-air missile system.

But a message on the official Twitter account of the Donetsk People's Republic had announced earlier that insurgents had seized a series of Buk systems capable of soaring to that height. That tweet was later deleted.

CNN also quoted an anonymous US defense official as saying that separatists have a Buk system. The official says it's unclear if the separatists captured it from Ukraine or Russia transferred it to them.

An anonymous military observer in China told the Global Times that hitting the passenger jet requires a medium or long range missile with radar guidance and a set of equipment. This may involve at least a dozen vehicles and dozens of personnel.

Where are the MH17 black boxes?

Ukraine's emergency services found two black boxes at the crash site, Interfax-Ukraine quoted Kostyantyn Batovsky, an adviser to the governor of Donetsk region, as saying. But the adviser said, "I have no information on the whereabouts of these boxes at the moment."

Earlier reports said rebels in the region claimed Thursday they had found one of the black boxes, and were sending it to Moscow, raising fears in the West that the data might be tampered with.

But the prime minister of the self-proclaimed Donetsk People's Republic Oleksandr Borodai stated Friday he cannot yet confirm the discovery of black boxes.

Russian Foreign Minister Sergei Lavrov told Russian state television Friday that the government does not plan to take the flight recorders. "We want international experts to get to the site of the crash as soon as possible so that they get the black boxes right away."

Why was a civilian plane allowed to fly over a conflict zone?

Russian news outlet Kommersant cited aviation sources as saying that flying across eastern Ukraine was "reckless," even at 33,000 feet (10,000 meters) and said Ukraine should have banned all flights over the area.

"It remains unclear how a Boeing 777 came to be above a conflict zone and why air traffic controllers didn't prevent a potentially dangerous situation," wrote Russian newspaper Rossiiskaya Gazeta.

Malaysia Airlines said Friday that it filed a flight plan requesting to fly at 35,000 feet throughout Ukraine airspace but was instructed by Ukraine air traffic control to fly at 33,000 feet upon entry.

AFP reported that a number of other Asian carriers had already abandoned the airspace over eastern Ukraine months ago because of security concerns.

South Korea's two main airlines, Korean Air and Asiana, as well as Australia's Qantas said they had all re-routed flights from as early as the beginning of the Crimea crisis.

Will international investigators be given full access to the region to carry out an objective probe?

Separatists said Friday they would welcome international and Ukrainian experts to the crash site, denying government reports they were preventing a search and rescue mission.

The Organization for Security and Cooperation in Europe later said about 30 of its staff had arrived at the scene by helicopter.

Reuters reported that FBI and US National Transportation Safety Board personnel are headed to the region to serve in an advisory role for the investigation.

US Transportation Secretary Anthony Foxx earlier said in an interview with MSNBC that the delay to the official investigators' access to the crash site was concerning.

Andriy Lysenko, a spokesman for the Information Analysis Center of the National Security and Defense Council of Ukraine, at a briefing in Kiev Friday also blamed rebels, who he claimed are "doing everything so that the investigation is not objective."

Was the recording showing rebels' taking responsibility authentic?

Ukraine released recordings of what they said was an intercepted call between an insurgent commander and a Russian intelligence officer as they realized they had shot down a passenger liner.

The Ukrainian Foreign Ministry sent reporters a link to the edited audio of the calls, with English subtitles, according to the New York Times.

According to the Kyiv Post, one phone call was made 20 minutes after the plane crash, in which the rebel reported to the Russian intelligence officer about the crash. The second intercepted conversation was made immediately upon inspection of the crash site. "It's 100 percent a passenger aircraft," one of them is recorded as saying, as he admitted to seeing no weapons on site. "Absolutely nothing. Civilian items, medicinal stuff, towels, toilet paper."

However, CNN and other media outlets said they cannot confirm its authenticity.