The French authorities say they may consider pressing the United States to have Zacarias Moussaoui serve his life sentence in France.
France and the United States are linked by two conventions on transferring convicts.
"An eventual request for transferring Mr Zacarias Moussaoui would be studied in this framework," the French foreign ministry spokesman said.
But he said no decision on transferring Moussaoui would be made until US authorities define the conditions of his sentence.
The justice minister, Pascal Clement, echoed that. "In France we have conditions that are specific, and we must know if they are compatible" he said on public television.
A US federal judge formally sentenced Moussaoui on Thursday after the jury recommended life in prison, instead of the death penalty.
Moussaoui, a Frenchman of Moroccan descent, was the only person charged in the United States in the September 11 attacks on New York and Washington that killed nearly 3,000 people.
"I don't think it's appropriate at this time to comment on that"
US attorney general
No formal request
The United States' attorney general, Alberto Gonzales, declined to say whether Moussaoui could be extradited to France.
"I don't think it's appropriate at this time to comment on that," he told a news conference in Vienna on Thursday after talks with European Union and Russian counterparts on security cooperation.
"Obviously there's been no formal request made, and with respect to a request by the French government, we would of course consider it at that time," he said.
Philippe Douste Blazy, France's foreign minister, later said in a statement that he had instructed the French embassy in Washington to "remain very attentive to the situation of Zacarias Moussaoui".
Moussaoui's mother, Aisha el Wafi, said her son would be living like a "rat in a hole" and accused France of siding with the United States during the trial.
"I feel there is a part of me that is dead, buried with my son who will be buried for the rest of his life at the age of 37 for things he hasn't done," she said.
"The whole world knows it now. France knows it too but France prefers to please the Americans anyway."
France provided information about Moussaoui to the US on condition that it could not be used in a sentence leading to the death penalty, which it abolished in 1981.
El Wafi's lawyer, Patrick Baudouin, expressed relief that the jury did not decide on the death penalty, and vowed a legal battle to bring Moussaoui home.
"They wanted to make the little soldier Moussaoui into a perpetrator of the September 11 attacks," Baudouin said. "He had no blood on his hands."
In Europe, Moussaoui's trial was widely considered less about terrorism than about what Europeans consider the perplexing American attachment to the death penalty.
Some French and Arab commentators also see Moussaoui as a scapegoat for a US administration eager to produce results in its increasingly discredited anti-terror war.