At least 49 people have died of thirst in a remote part of the Sahara desert in northern Niger after the truck carrying them broke down, authorities say.

The group were returning from Mali, where they had attended celebrations for the Muslim festival of Eid al-Adha, when they ran out of water, stranded more than 80 km (50 miles) west of Assamaka, a major border crossing point between Niger and Algeria.

"The travellers found themselves trapped in the heart of a hostile environment where extreme temperatures and lack of supply points make survival extremely difficult," said the governor of Agadez.

Only two survived, trekking across the desert to Assamaka, where they alerted authorities.

"This is something we have been working against, for years," Chehuo Azizou, the head of a local NGO, told the BBC.

"We have been sensitising drivers, travellers, and any person involved immigration activities, about the risk of crossing the desert. This recent incident is not unusual. Generally, we witness such cases on the route heading to Libya or Algeria".

In this latest case, the lorry had departed from the Malian town of Telhandek but veered away from its intended route, the Agadez governor's statement said.

The driver and passengers made repeated attempts to repair the vehicle over several days, but their efforts ultimately proved unsuccessful.

"Deprived of water and unable to repair the vehicle" most were unable to survive, the statement added.

"Dozens of lifeless bodies were found under the immobile truck and in its surroundings," it said.

The victims, all nationals of Niger, were buried in mass graves by the rescue team dispatched to the area by local authorities.

While returning from the scene, the rescue team said it came across another broken-down lorry carrying more than 60 people, who had been stranded for three days after a battery failure.

The lorry had set off from the Malian town of Harouba, more than 300km (186 miles) from the Niger border, the governor said in a follow-up statement.

The rescue team, which included Nigerien troops, distributed water to the "exhausted and distressed travellers" and helped repair the vehicle, allowing them to safely resume their journey.

The Niger desert remains a major transit corridor for migrants from across West Africa trying to reach Europe, repeatedly defying the risks associated with the perilous journey.

The governor of the nearest city, Agadez, said the tragedy underscored the "vulnerability of young people engaged in migratory and cross-border economic activities, often forced to pass through unstable areas in order to survive or seek better living conditions".