Hezbollah is no longer denying thousands of its fighters are helping to prop up Assad’s forces.

BEIRUT (WaPo) — Thousands of Lebanese Hezbollah militants were massed around the northern Syrian city of Aleppo on Sunday, according to rebels and a senior commander in the Lebanese Shiite movement, broadening Hezbollah’s backing of President Bashar al-Assad’s forces and stoking fears of an imminent assault on the city.

The commander, who spoke on the condition of anonymity because he is not authorized to talk to the media, said there were about 2,000 Hezbollah fighters in Aleppo province, largely stationed in Shiite towns north of the city. The rebel Free Syrian Army said Hezbollah forces had gathered in a suburb of the city Sunday and appeared to be preparing for an attack.

Rebels have secured swaths of Aleppo — Syria’s commercial capital and most populous city — since fighting engulfed it last summer, but the two sides have been locked in a grinding stalemate for months. An assault on the city could stretch rebel forces, which have sent reinforcements from Aleppo to fight against Hezbollah and Syrian troops in the battle for the town of Qusair, near the Lebanese border.

“The Aleppo battle has started on a very small scale; we’ve only just entered the game,” said the Hezbollah commander in an interview in Beirut on Saturday while on leave from fighting in Qusair, where he oversees five units. “We are going to go after strongholds where they think they are safe. They are going to fall like dominoes.”

He said the militants were largely concentrated around the Shiite towns of Zahra and Nubol, which have been under siege from largely Sunni rebel forces. A spokesman for Hezbollah said he could not confirm or deny their presence.

Louay al-Mokdad, political and media coordinator for the Free Syrian Army, said Hezbollah militants had gathered at a military academy in Aleppo’s western district of Hamdaniyah on Sunday. He put the number of the Shiite movement’s soldiers in the area at 4,000, quoting rebel intelligence.