Nigeria and Switzerland have signed an agreement that paves the way for the return of more than $300 million confiscated from the family of the Nigeria’s former military ruler, Sani Abacha, the office of Nigeria’s vice president said on Tuesday.

Transparency International, a corruption watchdog, has accused Abacha of stealing up to $5 billion of public money during the five years he ran the oil-rich country, from 1993 until his death in 1998.

Laolu Akande, a spokesman for Nigerian Vice President Yemi Osinbajo, said Nigeria’s attorney general signed a letter of intent, under the terms of which Switzerland will award Nigeria $321 million “acquired by the Abacha family,” Akandesaid in an emailed statement.

Swiss authorities said the letter of intent was also signed by its head of the Federal Department of Foreign Affairs, Didier Burkhalter, and “marks an important step toward the return of assets monitored by the World Bank”.

Nigerian President Muhammadu Buhari, who took office last year, has made combating corruption a priority. He has asked Britain and the United States for help recovering money stolen by some of the country’s elite over several years.

An economic crisis in Africa’s biggest economy and oil producer, brought on by a plunge in crude prices, has made the need to recoup money lost to corruption more acute.

In 2014, Nigeria and the Abacha family reached an agreement for the West African country to get back the funds, which had been frozen, in return for dropping a complaint against the former military ruler’s son, Abba Abacha.

He was charged by a Swiss court with money-laundering, fraud and forgery in April 2005, after being extradited from Germany, and later spent 561 days in custody. In 2006, Luxembourg ordered that funds held by the younger Abacha be frozen.