Officials said the U.N. international staff has relocated to Tunisia, CNN reported Monday.
Libyan officials reportedly apologized for the attack on the building.
Saif Gadhafi was killed in an airstrike Saturday. Three of his children were reportedly killed in the strike.
Elsewhere in Libya, witnesses reported the port city of Misurata, under seige for two months, was receiving heavy shelling by Gadhafi forces.
Pro-Gadhafi Libyan television said the port is being shelled to stop NATO from delivering weapons to rebels, who said the ship was trying to unload humanitarian aide.
The attack on the U.N. building by the Gadhafi regime indicates Libya had "once again breached its international responsibilities and obligations," said U.K. Foreign Secretary William Hague.
Hague give Libyan ambassador Omar Jelban 24 hours to leave the country.
"The attacks against diplomatic missions will not weaken our resolve to protect the civilian population in Libya," Hague said.