Damja added that the site had been sealed off and that no group has claimed the attack so far.
"My understanding is that there were two or three attackers who moved in on the administrative building", Otman Gajiji, a former chairman of the electoral commission, said to The New York Times.
The government in Tobruk, which is supported by self-proclaimed Libyan national army led by Field Marshall Khalifa Haftar, refuses to recognize the Tripoli-based unity government led by Fayez al-Serraj.
The BBC reports Wednesday's attack was the deadliest the country has seen in years. US and other Western intelligence and security officials think the Islamic State is seeking to regroup in the south as well as gain ground in nearby countries such as Tunisia, Mali and Niger.
Libyan and Western officials say they are concentrated in remote desert areas, but also have sleeper cells in coastal cities.
The Islamic State militant group said in an online statement that its fighters targeted the election head office.
02 de mayo de 2018, 15:49Cairo, May 2 (Prensa Latina) Egypt today strongly condemned the attack perpetrated against the Libyan Electoral Commission, in Tripoli, in which at least 16 people were killed. No date has been set for the elections. Egypt works to restore security and stability in Libya, defeat terrorism in the neighboring country and reach a national political consensus, stresses the text.
The bombing was the latest turmoil to strike the country in recent weeks. Rumors of his death spread like brushfire and triggered a potential succession struggle.