Assad 'has been warned' on Idlib chemical use: Mattis

US Defense Secretary Jim Mattis stressed Tuesday that Syrian President Bashar al-Assad has been well warned against any chemical weapons use in an anticipated assault on Idlib province.The Assad regime has twice been targeted by US air and missile strikes after previous alleged chemical attacks, and US officials have in recent days said additional action would follow if Assad were to use the banned weapons in rebel-held Idlib."In Idlib, we're watching very closely what the Assad regime, aided an