Dersi was appointed shortly after an attack on the US consulate on September 11 which cost the lives of US ambassador to Libya Chris Stevens and three other Americans.
He had occupied leading posts under the regime of Muammar Gaddafi, including post of anti-drugs chief, before joining the revolt against the former dictator when it started in February 2011.
Several recent assassinations in eastern Libya, mostly of police or army officers who served under Kadhafi, have been attributed to radical Islamists.