Peru's Prime Minister Salomon Lerner looks on before the cabinet's first presentation to congress in Lima in this August 25, 2011 file photo. [Photo/Agencies]

LIMA - Peruvian Prime Minister Salomon Lerner stepped down Saturday, and was succeeded by Interior Minister Oscar Valdes.

No reason was given publicly for his departure, but local news reports suggested it was probably triggered by his failed bid to end recent mass protests that stalled the Conga gold mining project worth $4.8 billion.

There was also speculation that President Ollanta Humala personally asked Lerner to quit in a bid to end tensions between the prime minister and other cabinet members.

Formerly a successful businessman of Jewish decent, Lerner was the campaign manager and a key player behind Humala's election in June.

His successor, Valdes, a 62-year-old former military officer, will have to continue the efforts to resolve the dispute over the country's biggest mining project.

Humala declared a state of emergency last week following mass rallies against the Conga project. The gold mining project, which involves moving water from four lakes high in the mountains into reservoirs the company would build, has met strong resistance from local peasants and officials in Cajamarca.