Well, it's indeed an Arab
Jambiya, from Yemen, as our Transilvanian Tiger has pointed out, and for the style of the hilt and what is left of the sheath, it may very well be a
Gusbi, from the coastal area of Hadramaut, at the south, bordering the Arabian Sea. The hilt of those is normally similar to the "mainstream" Arab
Jambiya, but the sheath has the peculiarity of curving very deeply upwards, featuring an elaborated chape that usually ends up at the same level or even higher than the hilt's pommel. The locket's decoration with red-coloured glass or stone ovals is also usual. A nice present, I must say
.
I also think the hilt it's rhino horn, by the way.
Some examples, from the Oriental-Arms website (for which one never may be grateful enough to Artzi):