Saudi Arabia has been staging what it says is the largest ever military exercise in the region. Twenty Islamic countries have been taking part, with thousands of troops deployed in the desert in northern Saudi Arabia, backed by tanks and warplanes. Saudi Arabia says it is currently facing two threats, one from so-called Islamic State (IS) in the north and from Yemeni rebels to the south, reportedly backed by Iran. Subscribe to BBC News HERE Check out our website: Facebook: Twitter: Instagram: