Germany confirmed today that it would deploy two batteries of Patriot missiles and 400 soldiers to its Nato ally Turkey, while stressing that the measure was strictly defensive.
Turkey asked Nato for the missiles last month, saying that it feared the Syrian civil war could spill over its borders.
A number of Syrian shells have landed on Turkish territory as its army battles rebel groups near the border.
Turkey has backed opposition forces seeking to overthrow the Bashar al-Assad government and is suspected of providing them with arms and platforms for foreign jihadists to cross into Syria.
Foreign Minister Guido Westerwelle said: "Nobody knows what such a regime is capable of and that is why we are acting protectively here."
But Syrian officials denounced the deployment as "provocative" and "psychological warfare" aimed at hampering attempts to defeat the rebels.
Deputy Foreign Minister Faisal Mekdad said the Patriot missiles and the "chorus" of Western worries over chemical weapons - which the US has said Damascus might use against its enemies - were part of a conspiracy to lay the foundations for military intervention.
"Even if such weapons exist in Syria they will not be used against the Syrian people," he said.
"Syria cannot commit suicide."
Fighting continued across the country today, with a car-bombing outside the Red Crescent headquarters in Damascus killing one.