Nouakchott -North African jihadist group Al-Murabitoun said it was holding a Romanian mineworker who was kidnapped in Burkina Faso last month, in an audio message released on Monday by Mauritanian media.
The Arabic recording, attributed to Adnan Abu Walid Sahraoui, named as the group's leader, called on "the Romanian government to give serious attention to negotiations for the release of the hostage held by the group".
The security officer was taken on April 4 when five armed men attacked a manganese mine in Tambao, 350km northeast of the capital, Ouagadougou.
The unidentified gunmen took off in the direction of the nearby border with Mali, according to security officials in both countries, with no group so far making a credible claim for the kidnapping.
"The Romanian government bears all responsibility for the fate of the hostage if it is slow to take the opportunity given to free its citizen," the recording claimed, in an apparent reference to Bucharest's unwillingness to engage in negotiations.
The message, which was released by Al-Akhbar - a Mauritanian news agency which regularly carries jihadist statements - ended with a reiterated pledge of allegiance to the Islamic State.
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This follows a similar pledge of allegiance from Sahraoui last week, which was immediately denied by the group's notorious Algerian commander Mokhtar Belmokhtar.
The disagreement appears to be the latest episode in a power struggle at the heart of Al-Murabitoun.
The organisation was formed in 2013 by the merger of the Signatories in Blood group, led by Belmokhtar, and the Movement for Oneness and Jihad in West Africa (MUJAO), which had been highly active in Mali's Gao region.
The contradictory statements have been interpreted as pointing to Sahraoui's rise and the possibility of a schism developing.
One-eyed Belmokhtar, a former chief of Al-Qaeda in the Islamic Maghreb, is wanted by the security services of several countries and is currently believed to be in southern Libya.
Kidnappings of foreigners, often for ransom, occasionally occur in Mali and Niger but not usually in Burkina Faso, a landlocked Sahel country.