BRUSSELS: Syrian armed forces fired a short-range ballistic missile on Sunday, bringing to more than 20 the number launched in the past month, NATO said on Monday.

NATO did not identify the missiles but their description fits that of the Scuds that are in the Syrian government's armoury.

"We've detected the launch of several unguided short-range ballistic missiles this month, including one on Sunday," NATO spokeswoman Oana Lungescu told reporters.

U.S. officials called Syria's firing of short-range missiles an escalation of the 21-month-old civil war when their use was first detected in December.

"Altogether over the last 30 days we've seen that over 20 short-range ballistic missiles have been fired by the regime forces," Lungescu said.

The missiles, apparently fired against opposition targets, landed in Syrian territory, mostly in northern Syria, she said. However, some of the missiles landed "quite close" to the Turkish border, she added.

The United States, Germany and the Netherlands are sending Patriot anti-missile systems to NATO member Turkey after Ankara asked for help to beef up its defences against possible missile attacks from Syria. The Patriot batteries are expected to be operational from around the end of January.