Two series of disappearances have been reported, in January and early March, and have raised tensions at a time when internationally isolated Mali is trying to foster closer ties between the two countries.

The Mauritanian authorities have given no details of what they think happened, but have accused the Malian army of "recurring criminal acts".

Unverified voice recordings posted on social media quote witnesses as blaming the Malian army for the disappearance of as many as 30 Mauritanians, and a Mauritanian MP said at least 15 people had been killed.

The experts have been sent to take part in a joint investigation, agreed to at the weekend after the Malian foreign minister visited the Mauritanian capital Nouakchott to try and de-escalate the situation.

The delegation, made up of police officers and military personnel, according to a security source, arrived Wednesday night.

They will begin their work "at the scene of the incident", the Mauritanian interior ministry said in a statement.

Malian government spokesman Colonel Abdoulaye Maiga previously said that "murders" had occurred and that Mali had opened an inquiry. But, he insisted, there was "at this point no evidence" to implicate the armed forces, "which respect human rights and always behave professionally".

Mali and Mauritania are key countries in the poor and troubled Sahel region of West Africa.

Mali is in the grip of a decade-old security crisis, with its poorly equipped armed forces struggling with jihadist insurgents, ethnic violence and criminal gangs.

A military junta seized power in August 2020, toppling elected president Ibrahim Boubacar Keita after a wave of public protests.

Last month, the government called for the immediate withdrawal of French troops stationed in the country.

The junta had been seeking closer ties with Mauritania to help ease the impact of an embargo by Mali's neighbours over failures to meet a promise to stage elections.