A Syrian human rights group says a key military unit loyal to President Bashar Assad is running secret prisons holding hundreds of suspected regime opponents.

The Syria-based Violations Documentation Center said in a report Monday that the regime's 4th Division runs detention centers in its bases in and around Damascus.

The division is commanded by Maher Assad, the president's younger brother. It is considered a pillar of loyalist forces and is charged with defending the capital.

The Center has tracked the dead, wounded and missing since the start of the uprising in March 2011.

The claims could not be independently verified. Syria's government rarely comments on claims by rights groups.

Other rights groups say tens of thousands of opposition members of their families have been detained during the two-year conflict.