The bodies of 92 people, almost all women and children, have been found in the Sahara desert. Rescuers said the people had died of thirst after their vehicle broke down during their attempt to reach Algeria from Niger.

An aid worker in Niger, a vast, landlocked country that straddles the desert between north and sub-Saharan Africa, told the Guardian that the scene was traumatic for the rescuers. They had discovered the bodies scattered in small groups around the desert.

"This is extremely difficult and the most horrible thing I have ever seen," said Almoustapha Alhacen, a rescuer who lives in Arlit, a uranium mining town 50 miles away. "These are women and children; they were abandoned and left to die. We found them scattered over a large area, in small groups. Some were lying under trees, others exposed to the sun. Sometimes we found a mother and her children. Some were children alone."

"They were left there for so long that their bodies are decomposed. Some of the bodies are still there."

The group was discovered after survivors reached Arlit on foot. Local experts said that the people were victims of human trafficking and were believed to have died two weeks ago as they tried to walk 12 miles in scorching sun to reach a well after the lorry they were travelling in broke down leaving them stranded.

Sources in Niger said that the group, who began their perilous journey across the desert in late September, was comprised of local people from Zinder, the second largest city in southern Niger, close to the border with Nigeria.

"We think that all these people are from the villages around Zinder," said Alhacen. "But until the investigation is finished, we cannot know all the details. It is very common for migrants to travel through this part of Niger. We have people from Nigeria and Burkina Faso, as well as people from Niger. They are trying to reach Libya and Algeria."

One security expert stressed that the group were not economic migrants but victims of trafficking.

Moussa Akfar, a security expert based in Niamey, Niger's capital, said: "This was in fact a case of poor people and children who were being trafficked to Algeria. There is an inquiry underway but we know that this was trafficking because economic migrants go to Libya – in Libya you find people of all nationalities, from Nigeria, Cameroon and other countries, heading to Europe.

"In this case all the victims were Nigerien from Zinder, and they were being trafficked. The questions that have to be asked now is how officials on road checkpoints did not alert the authorities about this group. There is endemic corruption at work."

Details are still emerging about what happened to the group. The discovery of the 92 people – they were known to be 32 women and 48 children among them, reports said – comes after a further 35 bodies were found this week.

The two groups were believed to be of the same set of migrants who were travelling north aboard two lorries in an attempt to reach Algeria.

They died in October, only six miles from the border between Niger and Algeria, after one of their two vehicles broke down and left them stranded as it headed off looking for replacement parts.

Niger security sources told the local press that 21 had survived, including two who had walked across the desert to Arlit, the nearest town and site of a plant for the French nuclear company Areva.

A further 19 who continued on their journey to Algeria and reached the town of Tamaresset, in southern Algeria, were turned away and repatriated back to Niger, local press reported.

The route taken across Niger's desert, which often begins in the southern town of Zinder and then proceeds through desert to the town of Agadez, is a well-known traffickers' route for transportations to north Africa.

Beyond the Sahara some people then try to board boats to Europe, while others end up in Algeria seeking work.

"Zinder and Agadez, these are the main migrant routes, as well as human trafficking routes in Niger," said Johnson Bien-Aime from the children's development organisation Plan Niger. "We know that trafficking is happening every day in these areas, but unfortunately, until now, nothing has been done about it."

Niger is one of the poorest countries in the world and has been rocked by repeated food crises in recent years. Last year Save the Children termed Niger the worst place in the world to be a mother amid its warnings that continuing poverty levels were driving people to undertake life-threatening journeys to higher income nations.

While many in Niger said that the October deaths were linked to trafficking, Algeria being the intended destination, Rhissa Feltou, the mayor of Arlit, said the group could have been trying to reach Europe.

"They were probably heading to the Mediterranean to try to go to Europe, or else to Algeria to work," said Feltou.

Rescue workers who found the bodies said the group could have included a party from an Islamic madrasa school, given the large number of children and an elderly man among the victims who appeared to be an Islamic teacher.

The plight of migrants from Africa and the Middle East is increasingly under the spotlight after a series of tragedies in which large numbers have died trying to reach Europe, including the 365 who perished off the Italian island of Lampedusa on 3 October when their boat capsized.

Tens of thousands of west African migrants, many of whom have paid as much as $3,000 to be taken across the desert from Niger to north Africa, arrive in Europe by sea each year, according to the United Nations.

"Sadly this is a typical migration that has been going on over last number of years," said John Ging, from the UN Office for the Coordination of Humanitarian Affairs. "We estimate that 80,000 make that journey every year from the Sahara, and basically they are economic migrants so impoverished they have to make these hazardous journeys."