Four Syrian towns that have been under crippling siege for more than two years are to be evacuated under a deal reached late on Tuesday, a monitoring group said.

Residents of Zabadani and Madaya, two towns near Damascus under siege by government forces, will leave their homes in return for the evacuation of Fuaa and Kafraya, two mainly Shiite towns in the northwest besieged by the rebels, the Syrian Observatory for Human Rights said. 

Observatory chief Rami Abdel Rahman said the deal was brokered by rebel supporter Qatar and government ally Iran.