* Niger top supplier of uranium to French nuclear industry
* Kidnapping threat has slowed investment (Adds comments from freed hostage, defence minister)
By Abdoulaye Massalatchi
NIAMEY, Nov 3 (Reuters) - Five African aid workers freed on Saturday after nearly three weeks as hostages in the Sahara desert said they were relieved to be back with their families in Niger and that their captors did not mistreat them.
A sixth aid worker - who was also kidnapped - was shot during the abduction in central Niger on Oct. 14 and later died of his wounds, they said.
"It is a feeling of joy and satisfaction now that we have been able to rejoin our families and friends, but there is a sadness as well, the loss of one of our colleagues," said Garba Yaye Issa, one of the aid workers, at a news conference in Niger's capital Niamey, hours after being released.
"We don't know where we were during our captivity. During that time, we were not mistreated either mentally or physically. We don't know who abducted us, but they spoke Arab as well as Tamashek and Hausa," he said.
Niger Defence Minister Karidio Mahamadou told Reuters he suspected the kidnappers belonged to an al Qaeda-linked group called MUJWA, which along with Ansar Dine has taken control of about two-thirds of Mali's north since a coup in March.
"The kidnappers were from MUJWA, no doubt," Mahamadou said. "Up to now, though, we have seen no claim of responsibility."
Gunmen kidnapped the six aid workers, who included five citizens of Niger and one from Chad, from the town of Dakoro in central Niger overnight on Oct. 14.
Officials said they believe the group were driven to a region of neighbouring Mali now in the hands of Islamists.
Gunmen linked to al Qaeda factions operating in the Sahel and Sahara zone have kidnapped people in Niger and taken them to Mali in the past, though they usually target Westerners for ransom payments.
The aid group that employed most of the kidnapped aid workers, BEFEN - which seeks to help women and children in the impoverished state - called the kidnapping and the death of worker Aime Soulembaye "an unjustifiable tragedy".
It said he was shot during the kidnapping and later died of his wounds, and it was now seeking to recover the body.
"We don't know the motivations of the kidnappers, but our concern at the moment is to repatriate the body of our deceased colleague and we pray for help and support in doing that," said BEFEN coordinator Sani Sayadi.
The Islamist takeover of the north of Mali has created a security vacuum and opened up a safe haven for extremists and organised crime groups in the Sahara desert.
The threat of kidnapping has slowed investment in Niger, the top supplier of uranium to France's nuclear power industry. French firm Areva delayed the planned start up of its Imouraren mine in Niger after seven of its workers were kidnapped in 2010.
Representatives from Niger's uranium exploration companies met President Mamadou Issoufou late on Friday to ask for tighter security in the northern desert.
"We explained all the difficulties we are facing in our work as a result of the security conditions," said Ibrahim Alasso, speaking on behalf of the companies. (Additional reporting and writing by Richard Valdmanis; Editing by Stephen Powell)