NATO says the first of six missile defense batteries sent to Turkey to intercept possible rockets fired from Syria is operational.
The alliance says the Patriot missile battery went "under command and control" in the southern city of Adana Saturday. The first battery was a Dutch unit.
The Netherlands and the United States are each providing two batteries of the U.S.-made Patriots. NATO expects to make the rest of the units fully operational in the next few days.
The Syrian government of President Bashar al-Assad has described the NATO Patriot deployment as a provocation.
On Friday, twin car bomb explosions in the Syrian-controlled part of the Golan Heights killed eight people. Government forces launched new raids in rebel-held districts of Damascus.
There was no claim of responsibility for the Golan Heights blasts, but car bombs and suicide attacks targeting Syrian troops are tactics commonly used by Islamic militants, who alongside the rebels are trying to topple Assad.
According to estimates, at least 60,000 people have been killed since the conflict began in March 2011. Hundreds of thousands more have sought refuge in neighboring countries.