Nigerian candidates in graft con

The EFCC has asked the public to inform on those asking for money

A number of Nigerian politicians have been conned out of thousands of dollars by people selling papers purporting to certify them as "corruption-free".

The scam follows a warning by Nigeria's anti-graft agency EFCC that anyone guilty of corruption would be banned from contesting next year's elections.

Conmen have been impersonating agency officials, donning dark suits to look the part.

But the EFCC says certificates are never given to those free of suspicion.

The BBC's Alex Last in Nigeria says that although the episode is embarrassing, it does go to show that the anti-corruption drive is seen as a real threat by some Nigerian politicians.

Nigeria is seen as being one of the most corrupt countries in the world.

The Economic and Financial Crimes Commission has asked the public to inform on anyone who claims to work for the agency who demands money for services.