BAGHDAD, May 20 (Reuters) - Iraqi forces thwarted an attack by Islamic State militants east of the city of Ramadi overnight, police and pro-government Sunni fighters in the area said. The insurgents attacked government lines in Husaiba al-Sharqiya, around halfway between Ramadi and the Habbaniya military base where Shi'ite paramilitaries have been gathering for a counter-offensive. (Reporting by Baghdad Bureau; editing by John Stonestreet)