The video, reportedly recorded last Wednesday, has been published on the Mauritanian news website Sahara Medias.
The hostages – Pierre Legrand, Daniel Larribe, Thierry Dole and Marc Feret – spoke to the camera individually in front of armed men wearing turbans.
They pleaded their case to French authorities, their families, and their employer, the French nuclear group Areva.
“It’s Wednesday, August 29 2012. We have now been here for nearly two years,” Larribe said without disclosing where he or his fellow hostages were.
Lagrand, the youngest hostage, said: “My family, I miss you very much. For 700 days, I have had no news from you. It’s difficult. I think about you every day and I hope to see you very soon.”
The men and three others were working for an Areva subsidiary in Arlit, northern Niger when they were captured by militants from Al-Qaeda in the Islamic Maghreb (AQIM) in September 2010.
Three of the hostages, including Larribe’s wife, were released in February 2011.
Sources say AQIM has demanded 90 million euros in ransom for the four, who in recordings released last April urged the then French President, Nicolas Sarkozy, to withdraw French troops from Afghanistan in line with the militants’ demand.
The current President, François Hollande, has sped up the withdrawal with 2,000 combat troops to be pulled out by the end of the year.
AQIM also kidnapped two Frenchmen, Philippe Verdon and Serge Lazarevic, in northern Mali last November.
Those men appeared in a separate video on Sahara Medias in mid August.