The agents who seized Lamido Sanusi's passport at Lagos airport Thursday said they were "acting on orders from the villa in Abuja," meaning Aso Rock Villa that is the president's office and official residence, said Nasir El-Rufai, a former minister for the capital territory who is now in the opposition.
Sanusi's lawyers are filing suit for alleged breach of his right to free movement and for threats of arrest and malicious prosecution without basis, El-Rufai told The Associated Press.
The spokeswoman for the State Security Service, Marilyn Ogar, did not respond to requests for comment.
President Goodluck Jonathan on Thursday ousted Sanusi, accusing him of "financial recklessness and misconduct." Critics say Sanusi was ousted because he exposed some USD 20 billion in missing petrodollars that they suspect could be used to fund campaigning for presidential and legislative elections next February.
Nigeria's naira currency, of which Sanusi was a staunch defender, immediately fell from 163 to 169 to the dollar, in what analysts said is the biggest fall since a 2009 devaluation.