A Paris court has rejected an appeal to release four Frenchmen who are under formal investigation in France after being released last week from the US naval base in Guantanamo Bay in Cuba.
The court upheld a ruling by another French court on Monday that the men could not be released because there was a risk they could flee, cause disorder or talk to each other.
They are being held on suspicion of "associating with criminals engaged in a terrorist enterprise".
Interior Minister Mr Dominique de Villepin called for a thorough investigation into whether the four had any links to terror attacks.
"It is very important to ask all the questions that the French people are asking themselves. What links with terrorist groups? What participation in, or association with this or that attack?" Mr Villepin told RTL radio on Wednesday.
"I think it's important to do everything to find the truth."
Mr Nizar Sassi, Mr Mourad Benchellali, Mr Imad Kanouni, and Mr Brahim Yadel were captured during the US-led war in Afghanistan in late 2001 and held by American forces on suspicion of fighting for the ousted Taliban government.
Their lawyers say they suspect their detention in France shows Paris is using the case to improve ties with Washington that were strained by its opposition to the Iraq war.
President Jacques Chirac has said French justice must determine their innocence or guilt. Three other Frenchmen remain in detention at Guantanamo.
Five Britons released from Guantanamo in March were freed within a day by British police without charges. A Danish citizen released this year now also lives as a free man.