The European Union urged Libyan authorities on Saturday to ensure the captured son of Muammar Gaddafi is brought to justice in full cooperation with the International Criminal Court.

Saif al-Islam, once tipped to succeed his late father as Libyan leader, has been arrested by fighters in the southern Libyan desert.

A spokesman for the EU's foreign policy chief Catherine Ashton said his arrest was a "significant development" that could help national reconciliation after a bloody civil war.

"The Libyan authorities should now ensure that Saif al-Islam is brought to justice in accordance with the principles of due process and in full cooperation with the International Criminal Court," Michael Mann said.

"It is important for future national reconciliation that those responsible for human rights violations committed both before and during the recent conflict are brought to justice."

The ICC issued arrest warrants for Muammar Gaddafi, Saif al-Islam and Libyan intelligence chief Abdullah al-Senussi on charges of crimes against humanity.