MALAYSIA Airlines said on Thursday it had "lost contact" with one of its passenger planes whose last known position was over eastern Ukraine, amid speculation it had been shot down.
"Malaysia Airlines has lost contact of MH17 from Amsterdam," the airline, still reeling from the disappearance of flight MH370, said on its Twitter account.
"The last known position was over Ukrainian airspace," it said, adding that it would provide more details soon.
The plane was due to travel from Amsterdam on an overnight flight to Kuala Lumpur, and was expected in the Malaysian capital at around 6:00 am on Friday (2200 GMT Thursday).
Ukrainian President Petro Poroshenko said the jet crashed over rebel-held eastern Ukraine and may have been shot down.
"We do not exclude that the plane was shot down and confirm that the Ukraine Armed Forces did not fire at any targets in the sky," Poroshenko said in a statement posted on the president's website.
Malaysia Airlines did not immediately specify the type of aircraft involved or how many passengers were aboard.
"I am shocked by reports that an MH plane crashed," Malaysian Prime Minister Najib Razak said on his Twitter feed.
"We are launching an immediate investigation."
The flag carrier and Malaysia's government are still struggling to provide answers to the mysterious March 8 disappearance of flight MH370.
The plane went missing with 239 passengers and crew on board and is now believed to have diverted off its flight path and crashed in the remote Indian Ocean.
No trace of the plane has yet been found.
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Malaysia Airlines ''loses contact'' with flight over Ukraine