A Malaysian airliner has been shot down over eastern Ukraine by militants on Thursday, killing all 295 people aboard.
A Ukrainian interior ministry official was quoted as saying by Interfax-Ukraine news agency.
Raising the stakes in the East-West showdown between Kiev and Moscow, the official blamed "terrorists" using a ground-to-air missile and Ukraine's prime minister called the downing of the flight from Amsterdam to Kuala Lumpur a "catastrophe".
A Reuters correspondent saw burning wreckage and bodies on the ground at the village of Grabovo, about 40 km (25 miles) from the Russian border in an area where pro-Russian rebels have been active and have claimed to have shot down other aircraft.
The Boeing 777 came down near the city of Donetsk, stronghold of pro-Russian rebels, interior ministry official Anton Gerashchenko said on Facebook, adding it was "shot down with a Buk anti-aircraft system by terrorists" - the term the Kiev government uses for militants seeking to unite eastern Ukraine with Russia. The dead were 280 passengers and 15 crew.
There was no further confirmation of the report, although Ukrainian officials said local residents had found wreckage.
Malaysia Airlines said on its Twitter feed it had lost contact with its flight MH-17 from Amsterdam. "The last known position was over Ukrainian airspace," it said.
Malaysia Airlines has lost contact of MH17 from Amsterdam. The last known position was over Ukrainian airspace. More details to follow.
— Malaysia Airlines (@MAS) July 17, 2014Gerashchenko was quoted as saying: "A civilian airliner travelling from Amsterdam to Kuala Lumpur has just been shot down by a Buk anti-aircraft system ... 280 passengers and 15 crew have been killed."
Interfax-Ukraine quoted another Ukrainian official as saying the plane disappeared from radar when it was flying at 10,000 metres (33,000 feet), a typical cruising altitude for airliners.
It came down at Torez, near Shakhtersk, some 40 km (25 miles) from the Russia border. The area has been the scene of fighting between Ukrainian troops and pro-Russian rebels.
Ukraine has accused Russia of taking an active role in the four-month-old conflict in recent days and accused it earlier on Thursday of shooting down a Ukrainian fighter jet - an accusation that Moscow denied.
Eastern Ukraine separatist leader Alexander Borodai says airliner shot down by Ukrainian government forces, Kiev denied involvement.
White House said US President Barack Obama directed senior US officials to remain in close touch with Ukrainian officials about downed plane.
According to RIA news agency, Russian President Putin discusses Malaysian Airliner crash in Ukraine with Obama over phone.
A rebel leader said Ukrainian forces shot the airliner down. Ukrainian official said their military was not involved.
The military commander of the rebels, a Russian named Igor Strelkov, had written on his social media page shortly before the report of the airliner being downed that his forces had brought down an Antonov An-26 in the same area. It is a turboprop transport plane of a type used by Ukraine's forces.