Niger has detained about 150 migrants crossing the Sahara desert to Algeria in a crackdown on illegal migration after 92 people, mostly women and children, died of thirst while trying to make the same journey.

The migrants, including 18 Nigerians, were arrested while travelling in a convoy of five vehicles, rescue worker Almoustapha Alhacena and a security official, who asked not to be identified, said on Saturday.

They were rounded up and have been placed in police cells in the northern town of  Arlit, a transit point for people seeking passage to Algeria, a security source told the AFP news agency.

"The migrants are being held at the gendarmerie but we do not yet know what will become of them," said the security source.

Niger mourns death of migrants

According to an aid group in Arlit, the group were travelling on board two lorries and three pick-up trucks.

Niger's government earlier announced it had "intercepted" 47 other migrants on Friday headed for Assamaka, the last town in Niger on the route to Tamanrasset, in southern Algeria.

This comes barely a day after the country ordered the "immediate" closure of migrant camps in the north of the country in response to the tragedy uncovered this week.

In the worst known incident of its kind in over a decade, and the worst ever in Niger, the decomposed bodies of 52 children, 33 women and seven men were found on Wednesday following their death in October, after two trucks carrying them broke down on the way to Algeria.

Twenty-one survivors

Prime Minister Brigi Rafini will pay a visit to the southern district of Kantche where most of the deceased came from, to present the "condolences of the nation wounded by this tragedy" to their families, according to the statement.

Niger's government also announced there would be three days of mourning following the tragedy.

Flags flew at half-mast on official buildings in memory of the victims, who all came from the south of the deeply poor west African country and were headed for Algeria.

Only 21 people survived out of 113 trying to cross Niger's desert border into Algeria.

The last disaster on such a scale was reported in May 2001 in Libya, back when it was ruled by Muammar Gaddafi and was a regional economic hub. On that occasion 140 people were found dead of thirst in the desert.

Since the fall of Gaddafi in 2011, the route via Agadez to Libya and on to Europe has gained popularity over the journey to Algeria.

More than 5,000 west Africans, many of them from Niger, took the Agadez trail each month between March and August this year, according to the United Nations.

Source: Agencies