The Syrian civil war is in its third year and the United Nations estimates that more than 70,000 people have died in the fighting and at least 1 million people have been displaced by conflict.
The U.N. Security Council has been sidelined by veto threats from Syrian allies such as Russia, who say draft resolutions lack balance. The Turkish government has Patriot missiles deployed along the border to protect against spill over, though NATO forces said there's no intention of imposing a no-fly zone over Syria.
Rasmussen told a Tuesday meeting of foreign ministers in Brussels that the situation in Syria was getting worse.
"We cannot ignore the risks of a regional spill-over with possible implications for Allied security," he said. "NATO has come to the support of Turkey with the rapid deployment of Patriots but we must continue to remain vigilant.
British Foreign Secretary William Hague said at a Friends of Syria meeting in Istanbul last weekend that the situation in Syria is "increasingly grave." In a statement Monday, he added that he was "appalled" by reports that more than 85 civilians died in government attacks on a suburb in Damascus.