"Yes, we will release the hostages unconditionally tomorrow. We are however working out details of their release to their employers," the spokesman said.
Police were forced to prevent an oppostion rally taking place during Tuesday's inauguration ceremony, reflecting disapproval of last month's election which was criticised by observers and prompted some parties to call for a re-run.
Heading off criticism of the election process, Olusegun Obasanjo, Nigeria's former leader, told Al Jazeera in his last interview before he leaves office that while the presidential election was "not perfect", it was in no way fraudulent.
Kalay Maistry, Al Jazeera's correspondent in Abuja, said that although there was a festive atmosphere at the swearing in ceremony, attended by many world and African leaders and dignataries, many Nigerians purposely avoided it.
Maistry said: "Elsewhere in Nigeria, people are staying at home and refusing to watch this because they are unhappy with the election results."
She said there were not many high-profile dignitaries at the event, indicating the level of unhappiness in Nigeria over the election.
Earlier on Tuesday, troops and police set up roadblocks and patrolled streets in volatile districts of Nigeria's biggest city, Lagos, saying opposition leaders would not be allowed to go ahead with a planned protest of the inauguration.Police said a coalition of labour and civic groups did not obtain an official permit for the protests planned in Lagos.
Lanre Ehonwa of the Civil Liberties Organisation, one of the civic groups supporting the protests, said the constitutional provision permitting public processions superseded a colonial law requiring police permits for rallies.
The 56-year-old Yar Adua won a landlside victory in last month's election and his inauguration will mark the first time in Nigerian history that power has transferred from one democratically elected leader to another.
But many observers say April's presidential poll was rigged to favour the PDP.Different character
Maistry said the quietly spoken Yar Adua was a very different character from his predecessor but was widely expected by many politicians and the public to be a principled man.
Previously a governor of the mainly Muslim Katsina state, his supporters say his track record of performance there endeared him to Obasanjo.
Many people see Yar Adua as a man of honesty, modesty and integrity, qualities that are considered rare in Nigeria, where politicians are often deeply involved in the country's almost endemic corruption.
Among the new president's immediate challenges are stemming rising violence in the oil-producing Niger Delta, the country's economic lifeline, and the threat of a strike over a fuel-price increase.
But perhaps the biggest test will be how he handles Obasanjo, who picked Yar Adua from obscurity six months ago to succeed him as the PDP's presidential candidate.
In the last days of his administration, Obasanjo has raised fuel prices by 15 per cent, doubled value-added tax and sold off two oil refineries to his business allies - moves that have angered the opposition and civil society groups.
Obasanjo denies accusations that he intends to run Nigerian affairs from behind the scenes.
He told Al Jazeera that he was described as a stooge when he first became president eight years ago.
"When I was running the affairs of Nigeria I was not a stooge of anybody."
Asked how he would like to be remembered, Obasanjo said: "When I had an opportunity to serve my country, I did my best."
Source: Al Jazeera and agencies