The United States said Friday it plans to deploy two Patriot missile batteries to Turkey along with 400 troops to help defend its ally against potential threats from neighbouring Syria.
The move was part of a wider NATO effort to bolster Turkey's air defences amid growing tension on the Turkish-Syrian border, with Ankara siding with opposition forces battling President Bashar al-Assad's regime.
US Defense Secretary Leon Panetta issued the order before landing at the Incirlik airbase in Turkey, his spokesman said.
"The secretary, as we are en route to Turkey, has signed an order that will deploy some 400 US personnel to Turkey to support two Patriot missile batteries," George Little told reporters aboard Panetta's plane.
"We expect them to be deployed in the coming weeks," he said, but declined to say where the batteries would be deployed.
At the Incirlik base, only about 100 kilometres (60 miles) from the Syrian border, Panetta called Turkey a key ally and said the deployment of Patriot batteries would ensure Ankara will "have the missile defence the may need."
Germany and The Netherlands also have agreed to provide advanced "hit-to-kill" Patriot weapons, which are designed to knock out cruise and ballistic missiles as well as aircraft.
On Friday, the German parliament approved by a wide majority the deployment of the missiles to Turkey, along with up to 400 German soldiers.
The move coincides with rising fears the Syrian regime may resort to using chemical weapons against rebel forces and after Assad's army unleashed Scud missiles in recent days.
Panetta renewed a US warning that the Assad regime must not use its chemical weapons against opposition forces, saying the United States was prepared to take military action if necessary.
He said the Pentagon had drawn up possible options to present to US President Barack Obama "as to what should be done ... should we get intelligence that's what they intend to do."
But he acknowledged that any attempt to secure or destroy Syria's chemical weapons would be fraught with danger.
"When you're dealing with this kind of stuff, you can't just simply go in there and blow it up," as bombing could trigger the release of chemical agents, he said.
"It's not easy," he added.
The Pentagon chief said his biggest concern was that the Assad regime might resort to chemical weapons in desperation.
"You can't imagine anyone who would do that to their own people. But history is replete with those leaders who made those kind of decisions, terrible decisions," he said. "So we have to be ready."
Turkey has vowed to defend its territory after cross-border artillery fire wounded civilians and following the downing of one of its fighter jets.
The Patriot batteries would not be useful for artillery or mortar fire but would be employed to thwart missile attacks.
The Patriot, or "Phased Array Tracking Radar to Intercept on Target", came into its own during the 1991 Gulf War when they were deployed to protect allies and US forces from Iraqi Scud missiles. The Patriot's boxy launch units became instantly recognisable in TV images of the conflict.
The anti-ballistic defence system was developed by arms manufacturer Lockheed Martin for the US Army.
Panetta flew to Turkey for a brief stop after a two-day visit to Afghanistan, where he consulted with commanders on future troop numbers.
But his tour was marred by a suicide bombing attack at Kandahar airfield in southern Afghanistan hours after he paid a visit to the NATO base on Thursday.
One US soldier was killed and three others were wounded in the blast. Seventeen Afghan civilians and one Afghan army soldier were also injured as the bomber detonated his vehicle near the huge airbase outside of Kandahar city.