Syria said on Friday a car bomb at a crowded gas station in Damascus was set off by "terrorists," a term it uses for rebels seeking to topple President Bashar al-Assad.
The blast on Thursday night killed 11 people and wounded 40 at a station packed with Syrians lining up for fuel, which has become scarce in the 21-month insurgency against Mr. al-Assad, in the second gas-station attack in the capital this week, opposition activists said.
Dozens of people were incinerated in an air strike as they waited for fuel at another Damascus gas station on Wednesday, according to opposition sources.
Meanwhile, U.S. soldiers who will man Patriot anti-missile batteries to protect Turkey from the spillover of the Syrian conflict began arriving in the NATO ally on Friday, the U.S. military said, but the missiles themselves are due later.
Turkey formally asked NATO for the missiles in November to bolster security along its 900-kilometre border with Syria.
Turkey repeatedly has scrambled fighter jets along the frontier and responded in kind when Syrian shells came down inside its borders, fanning fears that the civil war could spread to destablize the region.
About 400 U.S. personnel and equipment will arrive over the next several days by U.S. military airlift, the U.S. European Command said on its website.
No U.S. Patriot missiles arrived on Friday, however, according to a military source, and it will be several weeks before the missiles, supplied by Germany and the Netherlands, get to Turkey.
The U.S. troops, who began arriving at Incirlik air base in Turkey, will man two U.S. Patriot batteries out of a total of six batteries that have been promised by NATO allies.
Fighting has forced 560,000 Syrians to flee to neighbouring countries, according to the United Nations, causing a growing humanitarian problem in the region.
Lebanon, a country which has so far tried to distance itself from the conflict for fear it will inflame sectarian tensions, approved a plan to start registering 170,000 Syrian refugees and ask international donors for $180-million in aid.
"The Lebanese state will register the refugees … and guarantee aid and protection for the actual refugees in Lebanon," Social Affairs Minister Wael Abu Faour said after a cabinet session on Thursday night.
Most Sunni-ruled Arab states, as well as the West and Turkey, have called for Mr. al-Assad to step down.
A Lebanese citizen who crossed into Syria through a mountainous frontier region said the army appeared to have withdrawn from several border posts and villages in the area.
Rebels controlled a line of border towns and villages north of the capital, Damascus, stretching about 40 kilometres from Yabroud south to Rankus, said the man, who did not want to be named and visited Syria on Wednesday and Thursday.
"The border is controlled by the Free Syrian Army rebels," he said on Friday, adding he had crossed through mountainous terrain, covered in parts by more than a metre of snow.
Rebels in the area reported that some of Mr. al-Assad's forces have pulled back to defend the main north-south highway linking Syria's main cities of Damascus, Homs, Hama and Aleppo, while others were sent to reinforce the northern approach to Damascus.