NATO Secretary General Anders Fogh Rasmussen says Syrian government forces are continuing to fire short-range ballistic missiles at rebel fighters, according to BBC News.
A NATO source told the Reuters news agency that surveillance had detected multiple launches of "Scud-type missiles" on Thursday morning.
Rasmussen said it was the "act of a desperate regime approaching collapse".
Last week, NATO and the U.S. said more than six missiles had been fired from the Damascus area into northern Syria. However, the Syrian foreign ministry strongly denied using such weapons.
The military is believed to have access to a range of artillery rockets and medium-range missiles, some capable of carrying chemical weapons. These include the Soviet-designed SS-21 Scarab and Scud-B missiles.
Speaking to reporters in Brussels on Friday, Dec 21, Rasmussen confirmed NATO and its allies had detected new launches of Scud-type missiles.
"We strongly regret that act," he said. "I consider it an act of a desperate regime approaching collapse."
"The fact that such missiles are used in Syria emphasizes the need for effective defense and protection of our ally Turkey," he added, referring to NATO's decision to deploy several Patriot missile batteries along the country's southern border with Syria.
On Thursday evening, U.S. officials also said forces loyal to President Bashar al-Assad had resumed firing ballistic missiles against rebel positions in recent days.
They said there was no indication that the missiles were armed with chemical weapons and had no information on any casualties.
Contacts inside Syria told the paper that one attack had taken place on Thursday near Maara, a town in a rebel-held area north of Aleppo, near Turkey. The missile reportedly missed its target and no-one was hurt.