A European rocket has launched a major satellite designed to expand telecommunications for the British military from the Kourou space base in French Guiana, flight operators said.

Skynet 5D -- the fourth in Britain's new generation of Skynet military satellites -- was taken aloft by a heavy Ariane 5 at 2149 GMT on Wednesday, Arianespace said in an Internet feed of the launch.

The 4.8-tonne satellite was partnered by a second payload, Mexsat Bicentenario, a 2.9-tonne telecoms satellite for the Mexican government.

The Skynet system is a public-private arrangement between Britain's Ministry of Defence and the space firm Astrium, which builds the satellites.

Under it, British forces pay an annual charge for which they are guaranteed bandwidth for their communications, and any surplus is sold to fellow NATO countries or other allies.

Skynet 5D is designed to provide coverage over the Middle East, Africa and Asia.