I need help

hi every body
I got an offer from Ministry of health as Medical officer in IGMH ..
they sent me 2 copies through email " soft copies " of
1-An offer " which i signed and sent back through email" 
2-An approved Pre-registration
my question is ..shall they send me a work permit before my arrival there ?
because the employer here is the MOH itself" means the government"  not another employer ..
I read many infos about this part and really its so confusing
the one from MOH told me that I ll get work visa at airport when i ll show them both offer and that approved pre-registration .
I read I can not get work visa without work permit ...
so please can any one tell me if i must ask them for work permit or i travel and get it there ?
NB: its written somewhere if the employer is the government itself then I'm eligible to apply for work permit through 15 days of arrival ..