The money was frozen in 2014 by a Swiss court after a legal procedure against his son, Abba Abacha.

Originally deposited in Luxembourg, it is a fraction of the billions of dollars allegedly looted during his rule from 1993 to 1998.

Recovering the "Abacha loot" has been a major priority for Nigeria.

President Muhammadu Buhari made the recovery of stolen assets a major part of his 2015 election campaign and this will be the largest yet.

Although an agreement to repatriate the money was signed in March, the Nigerian Ministry of Justice, the World Bank and lawyers from Switzerland and the US have been grappling with legal complications surrounding the return of the money, says the BBC's Stephanie Hegarty in Abuja.

However on Monday, Switzerland announced that the battle was over and that the money will finally be returned.

It didn't say precisely when, but it did say that the World Bank must be involved in supervising how the money was spent, to ensure it was used "for the benefit of the Nigerian people".

"The fight against corruption is one of Switzerland's priorities" Swiss Foreign Minister Didier Burkhalter said, adding that the move should "strengthen social security for the poorest Nigerians", AFP reports.