BEIRUT (Reuters) - The U.S.-backed Syrian Democratic Forces (SDF) has taken the National Hospital in Raqqa, one of Islamic State s last remaining bastions in its former Syrian capital, a militia spokesman said on Tuesday.  The SDF, an alliance of Kurdish and Arab militias, is now fighting Islamic State in the area around Raqqa stadium, said the spokesman Mostafa Bali in a message.   During these clashes, the National Hospital was liberated and cleared from the Daesh mercenaries, and 22 of these foreign mercenaries were killed there,  said Bali.  The stadium is the last major position held by Islamic State after four months of battle in Raqqa and the departure of some of its fighters under a deal on Sunday, leaving only foreign jihadists.  Islamic State has lost swathes of its territory in Syria and Iraq this year, including its most prized possession Mosul, and in Syria it has been forced back into a strip of the Euphrates valley and surrounding areas of desert.  The SDF has been supported by a U.S.-led international coalition with air strikes and special forces operating on the ground since it started the fight for Raqqa in early June.  