"The attack resulted in the martyrdom of brother 29-year-old Saif al-Arab Gaddafi and three of the leader's grandchildren," official spokesperson Moussa Ibrahim told reporters in the wee hours.
"The house of Mr Saif al-Arab Gaddafi was attacked tonight with full power. The leader (Muammar Gaddafi) with his wife was there in the house with other friends and relatives," he said.
The spokesperson noted that the Libyan leader escaped unhurt.
"The leader himself is in good health, he wasn't harmed." Muammar Gaddafi's wife was also unharmed but other people in the house were injured.
"This was a direct attempt to assassinate the leader of the country."
According to reports, the building was extensively damaged and one unexploded bomb remains at the site.
Saif al-Arab was the youngest of Gaddafi's six sons.
An international coalition began carrying out strikes on forces loyal to Gaddafi on Mar 19 under a UN resolution to protect civilians in Libya. NATO took over the operations on Mar 31.