Earlier on Friday, al-Bolani told a press conference that the charges were baseless and politically motivated by those trying to undermine the interior ministry.
Speaking before the detainees were released, Abdul-Karim Khalaf, a spokesman for the Iraqi interior ministry, said a number of people had been arrested following a tip-off that they were members of al-Awda - or "Return" - a Sunni underground movement founded in 2003 with the aim of restoring Saddam and the Baath party to power.
"So far, charges have not been raised against anybody," he said, saying it was normal to detain people in relation to matters of national security.
"Such behaviour is not confined to Iraq only, it may happen anywhere in the world. When an issue threatens the security of a country, measures like the ones we did would be taken," he said.
Over a period of five days, dozens were rounded-up on conspiracy charges - including several high-ranking officials.
However, other Iraqi officials vigorously denied those arrested were involved in plotting a coup.
Brigadier-General Alaa al-Taei, the interior ministry's head of public relations, said those detained were not accused of planning a coup, but of planning to burn down the ministry in a possible attempt to destroy evidence against them.