LONDON (Reuters) - Britain is offering France further assistance in its military operations against Islamist rebels in Mali, but will not take a combat role, Prime Minister David Cameron's spokesman said on Monday. Cameron spoke to French President Francois Hollande late on Sunday about the conflict in the West African state, where French and Malian government forces are battling Islamist insurgents. Britain has already provided two C-17 military transport aircraft and a Sentinel surveillance plane to the operation. ...