Nato's Secretary-General has urged the release of four International Criminal Court (ICC) delegates detained in Libya amid a conflict over who should be responsible for the trial of Muammar Gaddafi's son.
Australian lawyer Melinda Taylor and Lebanese-born translator Helene Assaf were detained last week along with two male colleagues.
The group was visiting Gaddafi's son Saif al Islam, who is being held by militia in Zintan, southwest of Tripoli, when they were taken on allegations of smuggling documents to the son of the toppled dictator.
During a visit to Australia Anders Fogh Rasmussen said: "I strongly regret that certain groups in Libya have arrested or withheld representatives of the International Criminal Court.
"I would urge them to release these individuals as soon as possible."
The ICC says the detention is illegal.
It has been joined by human rights groups and Australia's government in demanding that the delegation be released, adding they should be given diplomatic protection while carrying out ICC work.
Those holding the group, however, are outside the control of the central government in Tripoli and want to hold the ICC members for at least 45 days while they are investigated for the alleged passing of letters to Saif al Islam from his fugitive right-hand man, Mohammed Ismail.
Ms Taylor's parents, John and Janelle Taylor, told Australian television their daughter had a long-held interest in human rights. She has worked for the ICC for nine years and had come under fire while working in Kosovo.
"All we want is the process of law to go ahead and for Melinda to be released as quickly as possible," Mrs Taylor said.
The detention comes amid a rift between the Netherlands-based court and the new government of Libya.
The ICC believes it should be responsible for the trial of Saif al Islam but Libya is protesting as leaders hold a firm belief he should be tried in his home country.
Libyan officials have previously promised a fair trial but the country still has the death penalty. The ICC's most severe punishment would be life imprisonment.
Saif al Islam was arrested in southern Libya in November last year as he was making headway to cross into neighbouring Niger.