BRUSSELS - Western powers warned Damascus Tuesday there would be an immediate reaction to any use of chemical weapons as the Nato military alliance agreed to deploy Patriot missiles along member state Turkey’s border as requested by Ankara to help it defend its territory against threats from Syria.

“The possible use of chemical weapons would be completely unacceptable to the whole international community and and I would expect an immediate reaction from the international community,” Nato head Anders Fogh Rasmussen said.

Syria’s chemical weapons stockpiles were “a matter of great concern,” Rasmussen said, adding: “This is also the reason why it is a matter of urgency to ensure effective defence and protection of our ally Turkey.” “Nato has agreed to augment Turkey’s air defence capabilities in order to defend the population and territory of Turkey and to contribute to the de-escalation of the crisis along the alliance’s border,” a statement said. Turkey formally asked its Nato partners to deploy the US-made anti-missile system after a series of cross-border shellings, including one that left five civilians dead on October 3.

“We say to anyone who would want to attack Turkey - don’t even think about it,” said Nato chief Anders Fogh Rasmussen, announcing the decision taken by the 28-member alliance.

Germany, the Netherlands and the United States have agreed to provide the Patriot missile batteries, which would come under the command of the Supreme Allied Commander Europe (SACEUR), the Nato statement said.

Stressing that the Patriot system was purely defensive, Rasmussen said technical discussions would now follow about how many of the US-made missiles would be deployed and where.

US President Barack Obama on Monday issued a new warning to Syrian President Bashar al-Assad not to use chemical weapons against his own people, as the conflict approaches the 21-month mark with more than 41,000 people killed.

“I want to make it absolutely clear to Assad and those under his command, the world is watching, the use of chemical weapons is and would be totally unacceptable,” Obama said.

“If you make the tragic mistake of using these weapons, there will be consequences and you will be held accountable.” France, with traditional interests in the region, made a similar point. “The leaders in Damascus must know the international community is watching them and will react” if chemical weapons are used, French foreign ministry spokesman Vincent Floreani said. The Syrian government, fighting to prevent the capital Damascus from falling to rebel forces, on Monday reiterated it would never resort to chemical weapons. Saudi Arabia meanwhile urged the international community to take a unified position on Syria after the rebel groups formed a coalition last month.

“We see in forming the new Syrian coalition an important positive step towards uniting the opposition under one banner,” Prince Saud al-Faisal said. “We hope to see a similar step towards uniting the positions and views of the international community in dealing with the Syrian issue,” the foreign minister added. Saudi Arabia has openly called for arming the Syrian rebels.

On the ground Tuesday, the Syrian army blasted a string of rebel zones on the eastern and southwestern outskirts of Damascus.

Rami Abdel Rahman, director of the Britain-based Syrian Observatory for Human Rights, said “the army is trying at all costs to keep the rebels out of Damascus. “The rebels are pushing hard to enter into the city but they have not been able to make the advance they are hoping for,” he added.

Pro-regime daily Al-Watan reported that the army is “making progress in all directions in Damascus province, chiefly in villages along the road linking the capital to the international airport.” Syrian state television meanwhile reported that a rebel attack on a school near Damascus on Tuesday killed nine students and their teacher.

In the face of deteriorating security, the United Nations on Monday suspended operations in Syria and said it would pull out non-essential staff, while the European Union reduced its activities in Damascus to a minimum.

Against this backdrop, Syria and Turkey’s request for help to boost its defence was dominating the two-day Nato meeting in Brussels, which was to dedicate some time also to strained ties with Moscow. Russian President Vladimir Putin pointedly warned Monday that deployment of the Patriots in Turkey would add to tensions and possibly widen the conflict.

“Creating additional capabilities on the border does not defuse the situation but on the contrary exacerbates it,” Putin said after talks in Istanbul.

Russian Foreign Minister Sergei Lavrov warned Tuesday that deploying Patriot missiles along Turkey’s border with Syria risked pouring more arms into the region, and dismissed fears of Damascus using chemical weapons.

Russia recognised Turkey’s right to ask for help from its Nato allies, Lavrov said, but added: “We are concerned that the conflict is being increasingly militarised.” “Any such deployment is creating the risk that these arms will be used,” Lavrov told journalists after a meeting of the Nato-Russia council.