NATO announced today that it will deploy Patriot anti-missile systems near Turkey's southern border, shoring up defences against the threat of cross-border attacks and bringing the United States and its allies closer to the civil war raging between Syrian rebels and President Bashar al-Assad's regime.

"We stand with Turkey in the spirit of strong solidarity," NATO Secretary General Anders Fogh Rasmussen told reporters. "To anyone who would want to attack Turkey, we say, 'Don't even think about it!"'

The alliance's 28 members decided to limit use of Patriots solely for the defensive purpose of warding off the mortar rounds and shells from Syria that have killed five Turks. But the announcement also appeared to be a message to the Assad regime at a time when Washington and other governments fear it may be readying its chemical weapons stockpiles for possible use.

Charles A. Duelfer, a former UN weapons inspector, told CBC News that Syria has two chemical weapons: a nerve and a mustard agent. Both are lethal and can be deployed on rockets or artillery shells.

He said that moving these weapons is troubling because Syria may be preparing to use them, and they become less secure the further they are from a base, meaning others could capture and use them for other purposes.

He said it is unclear why Assad is moving the weapons.

“It’s hard to get inside his head," he said. "But certainly he’s sending a strong signal.”

On Monday, U.S. officials said the White House and its allies were weighing military options to secure Syria's chemical and biological weapons.

Patriots are defensive weapons

Fogh Rasmussen stressed that the deployment of the Patriot systems — which include missiles, radar and other elements — would in no way support a no-fly zone over parts of Syria nor aid any offensive operation against the Arab state.

A Turkish soldier takes up position last week near Syria's border. Turkey has asked for NATO to provide Patriot anti-missile systems for the Turkey-Syria border. (Laszlo Balogh/Reuters)

But the decision to deploy the systems takes the U.S. and its European partners closer to the war, with the possibility of U.S.-made and alliance-operated hardware being used against the Assad regime for the first time.

Officials say the Patriots will be programmed so that they can intercept only Syrian weapons that cross into Turkish airspace. They aren't allowed to penetrate Syrian territory pre-emptively. That means they would have no immediate effect on any government offensives — chemical or conventional — that remain strictly inside Syria's national borders.

Still, Fogh Rasmussen insisted that the weapons could help de-escalate tensions along a border across which tens of thousands of Syrian refugees have fled and which has emerged as a critical transit point for weapons being smuggled to the rebels fighting to overthrow Assad.

Germany and the Netherlands are expected to provide to Turkey several batteries of the latest PAC-3 version of the U.S.-built Patriots air defence systems, which is optimized to intercept incoming missiles. The U.S. would likely fill any gaps, possibly by sending some from its stocks in Europe.

But the exact details of the deployment and the number of batteries are still to be determined by NATO. A joint team is studying possible basing sites in Turkey, and parliaments in both Germany and the Netherlands must then approve shifting assets and the possible involvement of several hundred soldiers.

Due to the complexity and size of the Patriot batteries, they cannot be flown quickly by air to Turkey and will probably have to travel by sea, alliance officials said. They probably won't arrive in Turkey for another month, officials predicted.

Fighting intensifies near Damascus

Meanwhile, a mortar slammed into a school in the Damascus suburbs on Tuesday, killing nine students and a teacher, according to state media.

Free Syrian Army fighters on Saturday were near buildings damaged by what activists said were missiles fired by a Syrian Air Force fighter jet in a Damascus suburb. (Thair Al-Damashqi/Shaam News Network/Handout/Reuters)

The state-run news agency SANA reported earlier that 29 students and one teacher had been killed, but later revised its report with the lower death toll. It blamed the attack on terrorists, the term the regime uses for rebels who are fighting to topple the government.

Also on Tuesday, Gunmen shot dead a journalist for a pro-government newspaper near Damascus, SANA said.

Reports from Britain-based opposition activist group Syrian Observatory for Human Rights emerged Tuesday of at least three killings — each of at least a dozen people — a day earlier.

The bloodshed comes as Syrian forces fired artillery at rebel targets in and around the capital.

With files from CBC News