Four French hostages who were kidnapped by al-Qaida in the Islamic Maghreb in northern Niger in 2010 have been released, President Francois Hollande said Tuesday.

"I have some good news. I just learned from Niger's president that our four hostages in the Sahel, the Arlit hostages, have been released," Hollande said on a visit to Bratislava.

Dozens of migrants from Niger heading for Algeria died of thirst in the Sahara desert after their vehicle broke down, local officials said Monday, while police said 19 survived.

"About 40 Nigeriens, including numerous children and women, who were attempting to emigrate to Algeria, died of thirst in mid-October," Rhissa Feltou, the mayor of the main northern town of Agadez, told Agence France Presse.

Niger has made the most progress worldwide on reducing child mortality since 1990, according to a study out Wednesday.

Also among the top 10 nations that have made the greatest strides in tackling such deaths are Liberia, Rwanda, Indonesia, Madagascar, India, China, Egypt, Tanzania and Mozambique, Save the Children found.

More than 2,500 children under five have died of malnutrition in Niger this year, the U.N. Children Fund said Wednesday.

The child mortality rate has declined over recent years but still stands at one percent and UNICEF said the impoverished west African was one of the world most aid-reliant countries.

Twenty people died, including 15 young children, when a boat on the Niger river broke up overnight near the central Malian city of Mopti, officials said Saturday, adding that another 23 people were missing.

"We don't know yet why the boat broke up," Commander Dramane Diallo, from the rescue services, told AFP.

Thousands of people in Niger protested Saturday against French nuclear firm Areva, which has been mining uranium in the impoverished country for nearly 50 years, one of the organizers said.

"The aim of the protest gathering some 5,000 people is to support the government in its upcoming discussions with Areva on the subject of our uranium," Azaoua Mamane told Agencec France Presse. Several other sources confirmed the turnout number.

Al-Qaida's north African branch has released a video purporting to show seven kidnapped Westerners, the Mauritanian news agency ANI reported, footage France's foreign ministry deemed "credible.”

The hostages are four Frenchmen kidnapped from a uranium compound in northern Niger exactly three years ago along with a Dutchman, a Swede and a South African who were abducted from Timbuktu in northern Mali in November 2011.

Severe flooding since the start of August in drought-prone Niger has killed at least 20 people and left around 48,000 homeless, the United Nations and local media reports said Wednesday.

The central Maradi region is the hardest-hit, with nine deaths and 19,425 people displaced, said the U.N., while four have been killed in the northern desert region of Agadez where rainfall has been unprecedented.

Severe flooding in drought-prone Niger has killed at least eight people, including seven children, and left around 2,000 homeless, authorities said Tuesday.

Four girls aged from two to five were killed as their homes in the central region of Maradi collapsed due to the heavy rains that have battered the west African nation since the start of the month.

Mauritania said Wednesday it would send soldiers to the United Nations peacekeeping force charged with ensuring security after elections in conflict-scarred Mali -- but only to areas near their shared border.

The MINUSMA force has replaced an African military mission which had been supporting French soldiers who entered Mali in January to halt an Islamist advance and to help the government re-establish its authority over the vast country.