A short-range ballistic missile was fired inside Syria on Wednesday, following similar launches last week, a NATO official said on Thursday.
The official condemned as "reckless" the missile launches, which US officials called an escalation of the 21-month-old Syrian civil war when their use was first spotted last month.
"The use of such indiscriminate weapons shows utter disregard for the lives of the Syrian people," he said.
The official said NATO had detected the launch of an unguided, short-range ballistic missile inside Syria on Wednesday, following similar launches on 2 and 3 January. All the missiles were fired from inside Syria and landed in northern Syria, he said.
The description of the missiles fits the Scuds that are in the Syrian military's armory, but the official said NATO could not confirm the type of missile used.
The NATO official was responding to a report from a Syrian opposition activist living near the Qaldoun army base, 50 km (30 miles) north of Damascus, who said four large rockets, apparently Scuds, were fired from the base overnight.
NATO has agreed to send Patriot anti-missile batteries to protect its member Turkey from possible missile attack from Syria.