The kidnapping of Nicolas Henin of Le Point magazine and TV journalist Pierre Torres on June 22 had not previously been made public.
Foreign ministry says images of seven hostages, including four French, being held by an al-Qaeda affiliate in the Sahel is fresh proof they are alive.
Islamist militant group Boko Haram was paid more than $3m before releasing a French family of seven, according to a Nigerian government report.
One of the men detained, a freelance photographer, managed to escape from the group who had taken him captive last November.
Recording shows man whose four children were kidnapped with him and other family members in Cameroon saying: 'We lose strength every day'.
After reports from a French government minister that they had been rescued, the fate of a family of seven kidnapped in Cameroon remains unclear.
A former US ambassador to Mali said Sarkozy administration paid vast ransom demands to the Islamists that French soldiers are now fighting.
A man claiming to be an al Qaeda militant held four people hostage in a bank in Toulouse, where gunman Mohamed Merah killed seven in March.