The United Nations Security Council has voted to increase the number of UN observers in Syria to 300 for three months.
A small team is already in Syria to monitor a ceasefire between government and rebel forces.
The resolution was unanimously approved by the Security Council after a debate about the conditions for their deployment.
UN Secretary General Ban Ki-moon will decide how and when they will be deployed.
The ceasefire began on 12 April.
Meanwhile, the monitors in Syria were allowed on Saturday to visit the city of Homs for the first time.
The BBC reports their visit came amid a lull in fighting in the city, which has been under bombardment by the army.
Rebels said tanks were temporarily hidden out of sight while the observers were in the city and that shelling was likely to resume.