* Latest rebel gains bring them closer to Assad's coastal areas * Hezbollah and Syria an**unce new gains along mountai**us border (Adds fighting around airport, army gains along Leba**n border) By Suleiman Al-Khalidi AMMAN, June 6 (Reuters) - Sunni Islamist groups have overrun Syrian army outposts and villages in the Idlib province, closing on coastal strongholds of President Bashar al Assad's government, rebels and a monitor said on Saturday. The Syrian army said its troops had abandoned the town of Muhambal in the western part of Idlib and were regrouping for a counter-offensive. The Islamist alliance, including al Qaeda's Nusra Front, calls its operation the "Army of Fatah", a reference to conquests that spread Islam across the Middle East from the seventh century.