NATO says it has approved Turkey's request to have Patriot missiles deployed on its territory to protect the country from possible attacks from neighboring Syria.
The move, which was widely anticipated, came at the end of a meeting of NATO foreign ministers in Brussels.
NATO Secretary-General Anders Fogh Rasmussen said the decision sent a clear message to anyone contemplating an attack.
"Turkey has asked for NATO's support and we stand with Turkey in the spirit of strong solidarity," Rasmussen said.
"To the Turkish people we say: 'We are determined to defend you and your territory.' To anyone who would want to attack Turkey, we say: 'Don't even think about it.'"
Rasmussen said that he expected the deployment to come "within weeks" after approval by NATO allies that possess Patriot missiles.
The 28-member alliance said in a statement that it welcomed "the intention of Germany, the Netherlands, and the United States to provide Patriot missile batteries, subject to their respective national procedures."
The United States, Germany, and Netherlands are the only countries that can deploy the missile systems.
Russia, a longtime Syria ally, has warned the deployment could aggravate hostilities.
But Rasmussen stressed that the deployment would be "defensive only" and would not support any offensive operation.
Rasmussen also warned the Syrian regime against the possible use of chemical weapons.
"The NATO ministers unanimously expressed grave concerns about reports that the Syrian regime may be considering the use of chemical weapons," he said. "Any such action would be completely unacceptable and a clear breach of international law."
Fighting was reported, meanwhile, in the southern suburbs of the Syrian capital, Damascus.
The Britain-based Syrian Observatory for Human Rights said on December 4 that battles were raging in the suburbs of Beit Saham, Akraba, Yalda, and near the Damascus international airport.
The group's director, Rami Abdel Rahman, said that "the rebels are pushing hard to enter into the city, but they have not been able to make the advance they are hoping for.”
The observatory relies on reports from activists on the ground.
Syrian state television said at least 28 students and a teacher were killed when a mortar shell hit their school.
State television said the rebels fired the shell at the school.
The Damascus suburbs have been opposition strongholds since the uprising began in March 2011.
In recent weeks, rebels have seized military bases, including some close to Damascus.
At least 40,000 people are estimated to have been killed in Syria since the beginning of the uprising.
With reporting by Reuters and BBC