Authorities said Thursday four suspects have been arrested and police were searching for a fifth man, CNN reported.
Deputy Prime Minister Awad al-Barassi said on Facebook the sexual assault occurred in front of the women's father. He said the sisters were born in Pakistan but are British citizens.
The women were working for a Turkish non-governmental organization that was involved in an aid convoy to Gaza.
Barassi said the family was stopped at a checkpoint Tuesday near Benina International Airport in Benghazi. They were abducted and the sisters assaulted.
A spokesman for the Libyan Interior Ministry said the family returned to Benghazi after the aid convoy was blocked from entering Egypt.
Barassi said he visited the family Thursday at the hospital where the women were being treated and apologized for the assault. He said they were in a "very bad psychological state."
LANA, the Libyan state news agency, reported that two members of the aid group are missing and others were assaulted at the checkpoint.
The Interior Ministry called the accused rapists "outlaws." Barassi said he hadn't determined if they belong to one of the militias working for Libyan security services.