A spokesman for Nigeria's former military ruler Gen Ibrahim Babangida has condemned the arrest of one of his aides over Friday's Abuja car bombings.
The detention of media mogul Raymond Dokpesi was "frivolous", Kassim Afegbua told the BBC.
Gen Babangida is running against President Goodluck Jonathan to be the governing party's presidential candidate in polls next year.
Officials say Mr Dokpesi had exchanged text messages with a key bomb suspect.
Messages from Henry Okah were found on Mr Dokpesi's phone, according to sources in the presidency.
Mr Okah has been charged in South Africa with terrorism in connection with the blasts, which killed at least 12 people, as Nigeria was marking 50 years of independence from the UK.
Mr Dokpesi is one of nine people arrested by Nigeria's security services over the attack.
The BBC's Caroline Duffield in Lagos says people in Abuja were stunned over his detention.
He owns the Africa Independent Television network and recently became Gen Babangida's chief of staff.
Mr Afegbua told the AFP news agency the arrest was a "political witch-hunt".
He was released without charge but is expected to be questioned again later on Tuesday.
Meanwhile, Mr Okah has been given his own cell in South Africa after expressing fears his life might be in danger.
He has denied any links to the blasts, but an e-mail purportedly sent by the militant group he once headed has said it had carried out the attacks.
If confirmed, this would be the first time Nigeria's oil militants have struck in the capital.
Nigeria's intelligence agency says it foiled an attempt to stage attacks in Abuja earlier last week.
South African prosecutors have described Mr Okah as the mastermind of the attack.
Mr Okah, who now lives in South Africa, is believed to lead a militant faction of the Movement for the Emancipation of the Niger Delta (Mend), opposed to a government amnesty for the oil-producing Niger Delta.
Most Mend commanders have joined the amnesty, set up to end years of unrest in the region which cut Nigeria's oil output by up to 20%.
Mend says it is fighting so that more of Nigeria's massive oil wealth is used to benefit the Niger Delta area which produces the oil.
But many criminal gangs also operate in the region, stealing oil and kidnapping people for ransom.