Justice Department officials have frozen nearly $500 million belonging to the late Nigerian dictator Sani Abacha in the largest-ever embezzlement forfeiture of a foreign ruler.

Abacha died in 1998. His five-year regime was named the fourth-most corrupt in the world by the nonprofit advocacy group Transparency International.

He was linked to the embezzlement of $5 billion of his nation’s funds for personal gain.

The asset freeze was part a DOJ initiative to seize the illicit gains of corrupt foreign leaders from domestic and international banks following FBI investigations.

The Abacha funds were recovered from bank accounts and investment portfolios, and the exact amount seized hasn't been determined, DOJ said Wednesday.

“Today’s action sends a clear message: We are determined and equipped to confiscate the ill-gotten riches of corrupt leaders who drain the resources of their countries," said Acting Assistant Attorney General Mythili Raman.

In addition to accusations of rampant corruption, Abacha's regime was widely condemned by the international community for human rights abuses.

Democracy advocates in Nigeria were tortured and abused for speaking out against the military’s rule, and Abacha gained international attention for the 1995 execution of activist Ken Saro-Wiwa.

During this violent reign, Abacha embezzled billions of dollars over several years from the Nigerian Central Bank by claiming the funds were integral to national security.

Abacha accomplished this by having his then-National Security Adviser Ismaila Gwarzo write fraudulent letters warning of imminent but unnamed threats to the security of Nigeria.

The letters would request millions of dollars at a time to be disbursed in the form of cash, traveler’s checks or wire transfers.

Abacha signed off on each letter, one of which cited a “desperate need” for “a lot of funds” due to the political climate of the country.

Another, dated November 1994, demanded $100 million “to combat an economy … deflected and distorted through the black market.”

Once the letter was received by the central bank of Nigeria, the funds were then withdrawn and placed into U.S. and European bank accounts by Abacha or one of his fellow conspirators.

Abacha also operated a debt buy-back scheme defrauding Nigeria of nearly $300 million during the same time period, according to court documents.

The dictator had the Nigerian government purchase its own debt back from companies held by Abacha at highly inflated prices.

The DOJ also seized five corporations once operated by Abacha and seven co-conspirators that were registered in the British Virgin Islands.

The conspirators are named in a civil lawsuit filed in the District Court for the District of Columbia. They assisted Abacha by setting up corporate entities which held accounts through which embezzled Nigerian money was funneled.

Court filings are available here.