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 wasfirst 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 following similar launches on January 2 and 3.
All the missiles have been fired from inside Syria and landed in northern Syria, he said.
The description of the missiles fits the Scuds in the Syrian military's armoury.
The Nato official was responding to a report from a Syrian opposition activist living near the Qaldoun army base, 30 miles north of Dam- ascus, who said four rockets were fired from the base.