UN chief Ban Ki-moon on Wednesday urged Syria's president Bashar al-Assad to desist from excessive use of force and to heed calls for reform.

"I urge again President Assad to heed calls for reform and freedom and to desists from excessive force and mass arrest of peaceful demonstrators," the UN Secretary General told journalists.

His comments came after activists said Syrian forces had tightened the noose on key protest hubs on Tuesday, including the flashpoint town of Banias, sealing off neighbourhoods and arresting dissident leaders.