U.S. Defense Secretary Leon Panetta has signed an order to send 2 Patriot air defense missile batteries and 400 American troops to Turkey as part of a North Atlantic Treaty Organization effort to protect Turkish territory from a potential cross-border missile attack by Syria.

The NATO military alliance on Tuesday agreed to the deployment of Patriot missiles as requested by member Turkey to help defend its border against threats from Syria.

There are nearly 70 American B61 nuclear bombs in Turkey. All of them are deployed on the Turkish Incirlik Air Base, Adana.

The Turkish Army staged tank exercises near the Syrian border on Wednesday, Turkish officials said, in a move highlighting Ankara's unease about security on the frontier.