An Ariane-5 rocket exploded soon after lift-off from French Guiana, sending two satellites plunging into the Atlantic ocean.
It is the fourth failure of an Ariane-5 in its 14-mission history, and is being seen as a major setback for the European space programme.
The rocket, which had been upgraded to launch payloads of up to 10 tonnes, lifted off as planned but the explosion occurred after three minutes.
Scientists are expected to give details of what went wrong at a news conference later today. The mission cost an estimated €600 million.
