A European Vega rocket carrying an Emirati satellite has been lost shortly after launching on Wednesday evening.
Arianespace, the French commercial space launch service, confirmed in a statement that "a launcher anomaly" two minutes after lift-off led to a "premature end to the mission".
Lifting off from a spaceport in French Guiana, the Vega rocket was carrying a military satellite for the United Arab Emirates.
It is believed to have crashed somewhere in the Atlantic Ocean.
In its statement, Arianespace said analysis of data was in progress "to clarify reasons for this failure".
It added: "An independent inquiry commission will be set up in the coming hours."
The failed mission was set to launch the first of two UAE systems into space, known as the FalconEye project.
But the launch of FalconEye1 was twice postponed due to weather, before Wednesday's doomed flight.
This is the first failure in 15 launches for Vega, a project joint developed by the Italian Space Agency and the European Space Agency.