NIAMEY (Reuters) - Sebastian Petronin sat slumped over a laptop watching a video of his mother, in a headscarf and looking frail and tearful, the latest proof the 72-year-old is alive nearly two years after she was kidnapped by jihadists and held in the Malian desert.

Now, fearing for her deteriorating health, he hopes her captors will allow him to visit her just once, even if there is scant chance he will be able to take her back.

“We are really concerned. She is a fighter but I feel like she has suffered blows to her morale that affected her,” Sebastian, 38, told Reuters as the video played in his hotel room in the Nigerian capital Niamey. “And I think she is very tired”.

Gunmen kidnapped Sophie Petronin in December 2016 in the northern Malian city of Gao, where she ran a charity for malnourished and orphaned children.

She is being held by fighters loyal to the main coalition of Islamist groups in the Sahara, the Jama’a Nusrat ul-Islam wa al-Muslimin (JNIM).

Her family has tried in vain to locate her and get her released, but in the last propaganda video, filmed and distributed to jihadist websites last month, she said something that rekindled hope.

“I would like to see you,” she told her son on the tape. “I know, for having shared in their (her captors’) lives for more than 17 months now that if they give guarantees, if they ensure that you can come in complete safety then you can believe them.”

Slideshow ( 3 images )

It was enough to launch Petronin on a mission to try to track her down that has taken him to parts of the Sahara as far afield as Mauritania and Niger, where he is meeting a negotiator he hopes can put him in touch with Sophie’s captors.

“The fact that the hostage takers allowed my mother to send me a direct message...is already quite unusual, even more so that she invites me to spend some time with her,” he said.

On one such trip into the desert, filmed by Reuters TV, he sat on the sand with a former acquaintance of hers, whose face was covered by a green turban.

“The desert is a huge territory but paradoxically a lot of people know each other,” he said. “And we can get hold of information even from a territory that is very far from here.”

French citizens are prime targets for kidnappers, both because of a perception that the government pays ransoms to get them out and because of their country’s role in the fight against Islamists.

France, former colonial master to most of the countries across the Sahara and the semi-arid Sahel just to the south, has 4,000 troops in a mission to try to crush the Islamist threat.

French President Emmanuel Macron was in Mauritania on Monday, a day after the attack on French and Mali forces in Gao. He said he would discuss ways of redeploying forces to better combat Islamist militancy after meeting the presidents of Mali, Niger, Burkina Faso, Chad and Mauritania, members of the G5 Sahel regional force that also came under attack on June 29.

Since France’s 2013 military intervention drove back al-Qaeda-linked groups that had seized cities and towns in northern Mali a year earlier, Islamist militants have repeatedly declared French citizens in West Africa to be targets.