The first of six Patriot missile batteries being deployed to the Turkey-Syria border was set up and put under Nato command on Saturday.
Provided by the Netherlands, the battery is meant to protect the Turkish city of Adan by shooting down missiles that could come over the Syrian border.
The US, Germany and the Netherlands are each providing two batteries of the US-made Patriots.
The other five will be set up in the next few days in Adana, Kahramanmaras and Gaziantep.
Nato insisted that the missiles were for defence only.
But Syria has not fired any surface-to-surface missiles at Turkey during a nearly two-year civil war and has described the deployment as a provocation.
Nato also deployed Patriot batteries to Turkey during the US-led invasion of Iraq 10 years ago.
They were never used and were withdrawn a few months later.
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