Senators voted unanimously on Thursday in support of the appointment of Farida Waziri, a retired high-ranking police officer chosen by Yar'Adua last month to head the Economic and Financial Crimes Commission (EFCC).

Yar'Adua took power a year ago pledging zero tolerance for corruption in one of the world's most tainted countries. But the removal of former EFCC head Nuhu Ribadu in December prompted campaigners to question his commitment to fighting graft.

Nigerian newspapers have reported that Waziri's appointment was sponsored by some ex-governors in Africa's top oil producer who are facing corruption and money-laundering charges.

This prompted allegations that the government had caved in to pressure from politicians anxious to stop investigations into their finances. National police chief Mike Okiro, who announced Ribadu's removal from the EFCC, has denied this.

The EFCC was prosecuting seven state governors from the previous administration when Ribadu was sent on a one-year policy and strategic studies course at a remote institute in central Nigeria.

Campaigners say there has been no significant progress in the cases against the former governors, two of whom helped finance Yar'Adua's election victory in April 2007.

The head of the United Nations crime office said in January that Ribadu's removal could hobble the crackdown on graft in Africa's most populous country, and send the wrong signal to EU donors who have poured $35 million into the project.