Lawyer Jacques Debray, in an interview published Monday, said he considers the arrest and imprisonment of his clients, Mourad Benchellali and Nizar Sassi, illegal.
"There will very likely be recourse against the United States for compensation," Debray told Le Parisien, without elaborating. "They are determined to fight."
Benchellali and Sassi were among four former Guantanamo detainees who were handed to French authorities on July 27 after authorities here negotiated for months to secure their release.
The suspects are jailed provisionally in France — a decision their defense lawyers formally challenged on Monday, said William Bourdon, another attorney for Benchellali and Sassi. Judicial officials must rule on the request by Wednesday,
This weekend, anti-terrorism judges placed the four men under investigation, a step toward formal charges, for "criminal association with a terrorist enterprise."
Investigators suspect they frequented groups that planned terror attacks in Europe. Several of the men confessed to training in military camps where they learned to use explosives and weapons, officials said.
Sassi, 22, and Benchellali, 24, are also under investigation for using false documents. The two are childhood friends who grew up in a tough suburb outside the central city of Lyon and went to Afghanistan together in June 2001 with stolen passports, officials say. They were arrested in December of that year and brought to Guantanamo.
The two have described mistreatment at the hands of U.S. authorities at Guantanamo, such as being threatened with dogs, struck in their cells or given sleeping medications, their lawyers have said.
"They (each) told me that separately," Debray told Le Parisien.
The other two French suspects, Imad Kanouni and Brahim Yadel, were also apprehended in the U.S. campaign that toppled Afghanistan's hard-line Taliban regime. They did not describe mistreatment at Guantanamo but said their lives were difficult there, lawyers said.
The camp at Guantanamo Bay holds about 600 inmates. The International Committee of the Red Cross and other human rights groups have expressed concerns about the U.S. military's practice of holding the prisoners at Guantanamo without charges.
France is still negotiating the release of three other French prisoners.
Meanwhile, five Moroccans detained at Guantanamo Bay, Cuba, were turned over to Moroccan authorities, the country's official news agency reported Monday.
The men, who were arrested during the U.S.-led war that toppled Afghanistan's hard-line Taliban regime, arrived in the North African kingdom on Sunday, the MAP news agency said. The five were handed to justice officials.
The prosecutor named the men as Mohamed Ouzar, 24; Mohamed Mazouz, 30; Radouane Chekkouri, 32; Abdellah Tabarak, 49, and Brahim Benchakroun, 24. They will be investigated by Moroccan police working under the prosecutor of the appeals court in Rabat, the capital.
Morocco, which has an active network of Islamic militants, is one of the United States' most important allies in the Muslim world in fighting terror.
Suicide bombings in Casablanca, Morocco's largest city, killed 33 bystanders and a dozen bombers in May 2003. Most of the suspects charged in the March 11 train bombings that killed 191 people in Madrid were Moroccans.
The kingdom has led a tough crackdown on Islamic radicals since the Casablanca bombings, arresting hundreds of suspects and sending their cases quickly through the judicial system.
The military prison camp at Guantanamo Bay now holds 586 inmates. Human rights groups have repeatedly expressed concerns about the U.S. military's practice of holding the prisoners at Guantanamo without charges.