INCIRLIK AIR BASE, Turkey -- Defense Secretary Leon E. Panetta signed an official deployment order Friday to send 400 U.S. military personnel and two Patriot air defense batteries to Turkey as its cross-border tensions intensify with Syria, where government forces have increasingly resorted to aerial attacks, including use of ballistic missiles, to fight a spreading insurgency.

The U.S. batteries will be part of a broader push to strengthen Turkey's defenses that will include the deployment of four other Patriot batteries -- two from Germany and two from the Netherlands. Each battery contains multiple rounds of guided missiles that can intercept and destroy other missiles and hostile aircraft flying at high speeds.

Mr. Panetta's deployment order, the result of NATO discussions last week, represents the most direct U.S. military action so far to help contain the Syrian conflict and minimize the risk that it will spill across the border with Turkey, a NATO member that is housing more than 100,000 Syrian refugees and providing aid to the Syrian rebels trying to oust President Bashar Assad.

Tensions between Turkey and Syria have escalated in recent months, as Syrian forces have bombed rebel positions along the border and occasionally lobbed artillery rounds into Turkish territory. The Turks have also grown increasingly alarmed that Mr. Assad's forces could fire missiles into Turkey.

News of the Patriot deployment order came as anti-government activists inside Syria reported fresh violence, including an unconfirmed rebel claim to have downed a government warplane attacking insurgent positions near the international airport in Damascus, the capital.

In Moscow, meanwhile, the Russian Foreign Ministry sought to distance itself from comments a day earlier by its Middle East envoy that the Syrian rebels may defeat Mr. Assad, a long-standing Kremlin ally and arms client. A ministry spokesman, Alexander K. Lukashevich, said Russia remained committed to a political solution in Syria. "We have never changed our position and will not change it," he said. He rejected a comment made by a State Department spokesman Thursday that Moscow had "woken up" and changed its position as dynamics shifted on the battlefield, saying, "We have never been asleep."

All six Patriot units deployed in Turkey will be under NATO's command and are scheduled to be operational by the end of January, according to officials in Washington.

"The United States has been supporting Turkey in its efforts to defend itself," Pentagon spokesman George Little said. The order "will deploy some 400 U.S. personnel to Turkey to support two Patriot missile batteries," he added, and the personnel and Patriot batteries will arrive in Turkey "in coming weeks." He did not specify their deployment locations.

After landing Friday at Incirlik, Mr. Panetta told a gathering of U.S. Air Force personnel of his decision to deploy the Patriots. He said the United States was working with Turkey, Jordan and Israel to monitor Syria's stockpiles of chemical weapons, and warned of "serious consequences" if Syria used them, but he did not offer any specifics. "We have drawn up plans for presenting to the president," he said. "We have to be ready."

Turkey's worries about vulnerability to Syrian missiles, including Scuds that might be tipped with chemical weapons, were heightened recently by intelligence reports that Syrian troops had mixed small amounts of precursor chemicals for sarin, a deadly nerve gas, at one or two storage sites, and loaded them into artillery shells and airplane bombs.

"Their arsenal of chemical weapons has been configured for use at a moment's notice," House Intelligence Committee chairman Mike Rogers, R-Mich., said in an interview Friday. Mr. Panetta, however, said this week that intelligence about chemical weapons activity in Syria had "leveled off."

The recent Scud missile attacks by Mr. Assad's forces against rebels in northern Syria have only added to Turkey's concerns. The Scud missiles were armed with conventional warheads, but the attacks showed that the Assad government is prepared to use missiles as it struggles to slow rebel gains.

Syria denied Thursday that it had fired Scuds this week. But NATO Secretary-General Anders Fogh Rasmussen said the intelligence gathered by the alliance indicated that they were Scud-type missiles. "In general, I think the regime in Damascus is approaching collapse," he said. "I think now it's only a question of time."

First Published: December 15, 2012, 5:00 a.m.