Nigeria is always ranked as one of the world's most corrupt countries

The authorities confirmed that the chief justice, Muhammadu Uwais, was among those questioned by the international police agency, Interpol.

The inquiry centres on allegations that a bribe of $30m was paid to the judges.

A spokesman for the Supreme Court said that the accusations were part of a detemined attempt to smear the image of the judiciary.

Opposition leaders have welcomed the crackdown as a step in the right direction.

A commission to fight corruption was one of the key bodies set up by President Olusegun Obasanjo soon after he came into office in 1999, but it has had little success so far in securing convictions.