French President Francois Hollande says three French soldiers have been killed in a helicopter crash near Libya's Benghazi during an intelligence-gathering mission.

The crash happened on Sunday. Libyan military officials would not comment on a report that the French soldiers were in a helicopter, but confirmed that four Libyans died in the crash.

The three French soldiers are the first confirmed Western military casualties since it became known this year that special forces were operating in Libya.

French special forces have been backing Libya's unity government, which has been battling Islamists and other opponents for more than two years. Its aircraft have been conducting reconnaissance flights since last December.