Several Scud missiles fired at rebels by Syria have landed "fairly close" to the Turkish border, NATO's senior military commander said in a blog explaining why Patriot anti-missile batteries are being deployed to Turkey.
Friday's comments by US Admiral James Stavridis, NATO's Supreme Allied Commander Europe, were the first to confirm that Scuds have come down near the border of Turkey, a NATO member state.
Stavridis also described the situation in Syria as "chaotic and dangerous".
US and NATO officials said on Wednesday that Syrian President Bashar al-Assad's forces had fired Scud-style ballistic missiles at rebels in recent days in what US officials described as an escalation of the 20-month civil war.
"Over the past few days, a handful of Scud missiles were launched inside Syria, directed by the regime against opposition targets. Several landed fairly close to the Turkish border, which is very worrisome," Stavridis wrote.
|US, Netherlands and Germany to send two Patriot missile batteries to Turkey [Al Jazeera]
Syria on Thursday denied it had used Scud missiles in its fight against what it calls "terrorist groups".
Stavridis voiced particular concern about Scuds because they can be fitted with chemical warheads. Syria is known to possess chemical weapons.
"Given a number of recent cross-border incidents with artillery and mortars landing in Turkey and killing Turkish civilians, we are concerned with possible Scud missile activity inside Syria. Scuds ... are particularly worrisome because they can carry chemical payloads," he said.
Turkey has scrambled jets along its frontier with Syria and responded in kind when shells from Syria landed inside its borders. If any Scuds strayed over the border into Turkish territory, it could carry the risk of spreading the conflict.
Ankara twice this year has invoked Article 4 of the NATO charter which provides for consultations when a member state feels its security is threatened.
NATO agreed last week to Turkey's request to send Patriots to reinforce its air defences against possible missile attack from Syria. The United States, Germany and the Netherlands are to send six Patriot batteries in all.
"Syria is clearly a chaotic and dangerous situation; but we have an absolute obligation to defend the borders of the alliance from any threat emanating from that troubled state," Stavridis wrote.
In-depth coverage of escalating violence across Syria
The alliance said sending Patriots was purely defensive and that it has no intention of intervening in Syria, but Russia said it was a step towards NATO involvement in the war.
Stavridis said the Patriots would help defend "the population centres in southern Turkey" and he said he would retain "operational command responsibility" for the Patriots.
"I anticipate we'll begin moving the systems toward Turkey very soon, and hope to have systems in place in the coming weeks after final national decisions are made and assets are allocated to NATO Command," he said.
The Netherlands, which is sending two Patriot batteries and up to 360 personnel to operate them, expects its missiles to be operational by the end of January, Dutch Prime Minister Mark Rutte said on Thursday.
Leon Panetta, the US defence secretary, signed an order on Friday to send two Patriot missile batteries to Turkey with 400 American personnel.
Also on Friday, Germany's lower house of parliament approved the sending of two Patriot batteries and 400 soldiers to Turkey as part of the NATO plan.