The United Nations - which backs a unity government based in Tripoli - said the attack "will not deter Libyans from moving forward".

By Rana Jawad, BBC North Africa correspondent

This attack is the deadliest and most elaborate of its kind in Tripoli in at least three years.

It may not come as a surprise, given Libya's precarious security conditions, but it will still have sent shockwaves around Tripoli because of the target and its reported victims, which included election commission employees.

In the past, attacks in the capital have mostly been confined to targeting security forces linked to the state or militias, as well as diplomatic mission buildings and foreigners.

The tactics used are reminiscent of the deadly attack on the Corinthia hotel in 2015 - in which nine people were killed.

The target appears to crystallise a political message on the future of the country and attempts to move forward.

But targeting the core symbol of that expected change for the country will not be taken lightly.