The Senegalese navy on Friday detained a boat near the northern city of Saint-Louis, the latest in a string of interventions over the last few months.

The West African country's army last week reported the interception of a boat carrying more than 250 "irregular migrants" from a number of African countries.

At least 25 people died on Monday when a different vessel capsized near Mauritania's capital Nouakchott, according to the Sahelian country's state-owned news agency.

A Europe-bound boat carrying around 170 people that set off from Senegal capsized off the Mauritanian coast in early July, killing nearly 90 people.

The disaster prompted Senegal's Prime Minister Ousmane Sonko to urge people not to risk the Atlantic Ocean's currents in overcrowded vessels that often are not seaworthy, and on which they do not carry sufficient drinking water.

But the route is increasingly used as authorities step up surveillance in the Mediterranean.

According to the Spanish NGO Caminando Fronteras, more than 5,000 people died trying to reach Spain by sea in the first five months of this year.

That represents the highest daily average toll since it began keeping records in 2007.