Allies of Mauritania's ousted leader have united to back a presidential candidate in March's elections.
Col Vall, who leads the military junta, is not standing in elections
Correspondents say this makes Sidi Ould Cheikh Abdallahi, an independent, favourite as the 18-party coalition holds a majority in parliament.
Leaders of the military junta which seized power in 2005 are not standing.
Some accuse Mr Abdallahi of being a front man for the junta, but he is not seen as being close to the military, former president or the opposition.
The BBC's Ahmed Salem in the capital, Nouakchott, says as a result he is regarded as an independent.
A total of 21 candidates have registered for the polls which are to herald a return to civilian democracy.
The former opposition is divided, fielding four candidates, but argue that Mauritania needs to break with its coup-ridden past.
A group of army officers staged a bloodless coup in 2005 when Maaouiya Ould Sid Ahmed Taya, who had seized power 11 years earlier, was out of the country.
The coalition backing Mr Adallahi - calling itself The Charter - warns that the opposition candidates could be a threat to Mauritania's stability.