Senior Nigerian judges arrested as part of a corruption investigation have been released, the head of the country's bar association and a security agency official said on Tuesday.



The Department of State Services (DSS), the country's security agency, on Saturday said it seized $800,000 in cash found during raids targeting judges from the supreme, appeal and high courts.



Abubakar Mahmoud, who heads the Nigerian Bar Association (NBA), on Tuesday said all of the judges held had been released, although he did not confirm the number or when they were freed.



A DSS official, who did not want to be named, said seven judges were released on bail on Sunday and reported to the security agency on Monday.



"I cannot say when they will be arraigned in court but as soon as we are done with investigations, we will send the files to the attorney general's office which will advise accordingly and act," said the official.



The judiciary has been the subject of longstanding corruption allegations but the nature of the raids has been criticized as being unconstitutional, with the NBA accusing the DSS of a "Gestapo-style operation".



President Muhammadu Buhari, a former military ruler, has pledged to crack down on corruption since taking office last year but critics say he is conducting a witch-hunt against his political opponents.



His spokesman said the raids were part of an anti-corruption drive and were not an attack on the judiciary.