(Reuters) - Islamist fighters seized dozens of Western and Algerian hostages in a dawn raid on a natural gas facility deep in the Sahara on Wednesday and demanded France halt a new offensive against rebels in neighboring Mali. Three people, among them one British and one French, were reported killed, but details were sketchy and numbers of those held at Tigantourine ranged from 41 foreigners - including perhaps seven Americans as well as Japanese and Europeans - to over 100 local staff, held separately and less closely watched. What is clear is that with a dramatic counterpunch to this...