BEIRUT — Rebels captured part of a sprawling Syrian army base outside the embattled northern city of Aleppo, tightening the opposition's grip on areas close to the Turkish border, activists said Monday.
The gains by rebel forces came as the European Union denounced the Syrian conflict, which activists say has killed more than 40,000 people.
"The current situation in Syria is a stain on the world's conscience, and the international community has a moral duty to address it," said European Commission president Jose Manuel Barroso.
The rebels also killed 13 soldiers in an ambush near a strategic northern town along a road linking Aleppo, the nation's largest city and business hub, with Damascus, and captured 20 soldiers and policemen at a major post on the highway linking the central town of Salamiyeh with the northern city of Raqqa, activists said.
Once on the defensive, Syria's rebels have gained momentum in recent weeks with a number of tactical advances, seizing airbases near Damascus and Aleppo and putting President Bashar Assad's forces on their heels.
In an interview with Dubai TV, Manaf Tlass, Syria's top military defector, said Assad's regime is "over," and he advised the president to leave office and let the country's people decide their own fate.
The Britain-based Syrian Observatory for Human Rights said the rebels entered the Sheik Suleiman military base outside Aleppo on Sunday afternoon, after weeks of fighting around the facility.
The observatory said the rebels who stormed the base belong to hard-line Islamic militant groups such as Jabhat al-Nusra.
The United States has designated the Jabhat al-Nusra group, which has alleged ties to al-Qaida, as a terrorist organization.
Also, the United States, taking a calculated risk that embracing chosen leaders of Syria's fragmented rebels will speed Assad's fall, will recognize the Syrian National Coalition, a slate of opposition figures, when American, European and Arab diplomats meet with its leaders in Morocco later this week.