The rebel Free Syrian Army said on Thursday it is making "every effort" to locate and release a group of Lebanese Shia pilgrims kidnapped in Syria's northern province of Aleppo.

"The leadership is making every effort to find out where the abductees are, and to make sure they are freed," FSA official spokesman Colonel Kassem Saadeddine said in a statement.

Saadeddine reiterated that the FSA had no involvement in this week's kidnappings, condemning "all kidnapping operations, regardless of their nationality or religious belief or sect".

At the same time, he complained over the treatment of Syrian refugees and anti-regime figures in Lebanon.

"Revolutionary Syrians in Lebanon have faced persecution, kidnap and murder," he charged. "We will no longer be silent on any action carried out by any Lebanese parties affecting Syrians in Lebanon."

The FSA spokesman urged "the Lebanese state to take full responsibility in hosting and protecting Syrian refugees in Lebanon," where the government is dominated by a coalition that supports Syria's regime.

Lebanon's state news agency on Tuesday reported that the FSA had abducted a group of Shia in Aleppo on a bus returning via Iraq and Syria from a pilgrimage to holy sites in Iran.

Syria's main opposition coalition has called for the prompt release of the group, blaming Assad's regime for a "security vacuum" in the unrest-swept country.

The Syrian National Council "does not think it is impossible that the regime is involved in this operation," in order to sow "disorder" in neighbouring Lebanon, the group said.

News of the kidnappings prompted their families and thousands of supporters to pour out onto the streets of Beirut's mainly Shiite southern suburbs on Tuesday night to demand their release.