A Nigerian anti-corruption agency has begun investigating former ministers alleged to have taken bribes from the German telecoms firm, Siemens.
The firm has faced a series of probes over corruption
Siemens was found guilty of paying bribes and was fined 201m euros ($248m) by a Munich court on 4 October.
Names on the court papers that emerged last week included Bello Mohammed Haliru, the late Haruna Elewi and Tajudeen Olanrewaju.
Dr Mohammed and Gen Olanrewaju have denied taking payments from Siemens.
The Independent Corrupt Practices and Other Related Offences Commission (ICPC) has summoned more than 10 officials for questioning into the affair, after President Yar' Adua ordered the security agencies to "take appropriate legal action".
The president's special adviser on communications, Olusegun Adeniyi, issued a statement giving an assurance from Mr Yar'Adua that "in this Siemens scandal, as in all cases that border on good governance and transparency, there will neither be sacred cows nor a cover up for anybody found culpable of breaching the law".
Siemens's own investigations uncovered more than 1.3bn euros in suspicious payments, 10m of which were said to have been paid to the Nigerian ministers or officials between 2001 and 2004.
The company's chairman and chief executive both quit over the scandal and at least two employees were given suspended sentences for bribery and breach of trust.
Siemens has accepted the Munich court judgement and has also agreed to pay 179m euros to the tax authorities.
However, it faces even higher fines in the United States if it is found to have systematically bribed its way into winning contracts.