The Pentagon has said it will send Patriot air defence missiles and 400 troops to Turkey as part of a Nato force meant to protect Turkish territory from potential Syrian missile attack.
Pentagon press secretary George Little said defence secretary Leon Panetta signed a deployment order today while en route to Turkey from Afghanistan.
The order calls for 400 US soldiers to operate two batteries of Patriots at undisclosed locations in Turkey, Mr Little told reporters.
Turkey is a founding member of Nato and requested that the alliance provide Patriots.
They will be sent by Nato members Germany and the Netherlands as well as the US for an undetermined period.