LIMA, Peru -- An official close to Peruvian Cabinet chief Salomon Lerner says he has resigned.

The official says some of Lerner's aides have also stepped down. He spoke on condition of anonymity due to the matter's sensitive nature.

Lerner had been campaign manager to President Ollanta Humala, who was elected in June.

He was recently involved in failed attempts to negotiate an end to protests that have stalled Peru's biggest foreign investment, the $4.8 billion Conga gold mining project.