"The General National Congress appointed Abdullah Al-Thinni as the prime minister under a condition of forming a government within week," he told Reuters.
Once a cabinet had been formed, the congress would decide whether Thinni and his minister could stay until a general vote expected for later this year, he said.
Earlier, Libya's cabinet has a sent letter to parliament asking for more power and a longer mandate, but denies reports it has resigned, a government spokesman said.
Television stations in Libya and across the Arab world, including Al Jazeera, ran reports earlier on Tuesday that the cabinet had stepped down.
REUTERS