NATO declared that a Patriot missile battery went operational on Turkey's border with Syria on Saturday, as a watchdog reported regime warplanes launched raids on a Damascus district.
Britain, meanwhile, pledged a multi-million dollar aid package to help Syrian civilians, nearly half of which would be channelled through agencies in Jordan where a record 6,400 refugees arrived on Friday.
The UN, which says the 22-month conflict has killed more than 60,000 people, estimates the number of refugees in Syria's neighbouring countries will double to 1.1 million by June, if the bloodshed continues.
In northern neighbour Turkey, NATO said one of six batteries of Patriot missiles deployed to protect against a spillover of the conflict went into operation on Saturday.
The battery, provided by The Netherlands, would "help to protect the (southern) city and people of Adana against missile threats," it said, adding the other five batteries should be ready in the coming days.
Ankara and NATO have stressed the deployment is for defensive purposes only, while Damascus and its ally Moscow have criticised the measure. The US-made missiles can take out cruise and ballistic missiles, as well as aircraft.
On the ground in Syria, the violence raged unabated on Saturday between rebel fighters and forces loyal to President Bashar al-Assad.
The air force raided rebel positions nationwide, including in an eastern district of the capital, the Syrian Observatory for Human Rights and activists said.
"Warplanes carried out three air raids on the outskirts of Hermela area in Jobar," reported the Local Coordination Committees, a network of opposition activists on the ground.
The Observatory, which relies on a network of activists, doctors and lawyers, reported strikes on Jobar and the outlying region of Eastern Ghuta, where rebels have their rear bases.
At least four civilians were killed in air raids on the northern rebel city of Al-Bab, while similar strikes were reported in Daraa province in the south.
Warplanes also bombed the opposition stronghold of Qusayr in central Syria, where nine rebels were killed defending the town against an army onslaught.
The insurgents are working to keep control of Qusayr and nearby Rastan after being largely driven from their position in Homs city, which suffered bombardments for the past half year and where more than 100 people died amid an army offensive in the last seven days.
Driven from large swathes of land in the north and east by rebels, the regime is focused on maintaining its grip on the key axis from Damascus to Homs, and on to the coastal Alawite heartland.
Troops have meanwhile been forced to relinquish vast stretches of territory in the north and the east.
Near the northwestern city of Idlib on Saturday, rebels freed more than 100 inmates as they battled troops at a major prison, the Observatory said, reporting 10 insurgents killed since the attack began the day before.
Unverified videos posted online by activists showed dozens of prisoners escaping to an outdoor area of the prison, protected by rebels, as gunfire and explosions are heard.
Other green night-vision footage apparently from inside the prison showed bombed-out cells and dead inmates on the floor. Prisoners said they were summarily executed by soldiers.
The rebels did not take control of the prison, located west of the regime-held provincial capital, the Observatory said.
International Development Secretary Justine Greening announced Britain's £21 million ($33 million, 25 million euros) of aid for Syrian civilians after a visit to Jordan's Zaatari refugee camp.
Greening implored other nations to step up aid at donor conference in Kuwait on January 30 to stem the humanitarian fallout from the brutal conflict that erupted in March 2011.
"Warm words won't provide the shelter and support that Syrian refugees need. Money will," she said. "This is a man-made crisis. That man is Assad."