Nigeria opposition, human rights and anti-corruption groups are criticizing what they call the harassment of the country's former anti-corruption chief, Nuhu Ribadu, by security agents. Ribadu was forced out of a graduation ceremony at a strategic studies academy in the northern city of Jos on Saturday. For VOA, Gilbert da Costa has more from Abuja.

Since his controversial removal as head of the Economic and Financial Crimes Commission last year, Nuhu Ribadu has remained in the news.

Ribadu, a senior police officer, was shot at by unknown gunmen while traveling between Jos and the capital city of Abuja recently.

Then he was demoted by the police authorities, forcing him to file a suit challenging the action.

And just last weekend, the celebrated anti-corruption fighter was forced out of a graduation ceremony by security operatives. Ribadu was one of the graduating students at the National Institute for Policy and Strategic Studies.

President Umaru Yar'Adua, who promised to tackle graft when elected in 2007, has been criticized for making slow progress on the issue.

The anti-corruption group Zero Corruption Coalition says the arrest and harassment of Ribadu is a huge setback for the anti-corruption campaign in Nigeria.

"I think it is the climax of the Yar'Adua government proving to the whole world that they are just not serious about anti-corruption," said Biodun Sowemi, who speaks for the group. "How do you tell an average policeman not to take bribe when Ribadu who is the symbol of anti-corruption in the Nigerian police force is being destroyed? He is being hunted and harassed in different ways. The powers that be, those Ribadu hunted when he was EFCC boss, the very powerful people, they are the ones nominating people who hold positions of power in Aso Rock [presidency] today."

The Economic and Financial Crimes Commission was created in 2003 to try to stamp out corruption in a nation ranked among the most corrupt.

The removal of Ribadu, its former head, triggered accusations President Yar'Adua lacks the political will to pursue top suspects, which he denies.

Under former president Olusegun Obasanjo, the EFCC, led by Ribadu, was accused of acting on his behalf, pursuing Obasanjo's enemies with zeal and turning a blind eye to corruption on the part of his cronies.