Stablecoin issuer Tether has frozen $225 million worth of its own stablecoin following an investigation by the U.S. Department of Justice (DOJ) into an international human trafficking syndicate in Southeast Asia.

The investigation was ongoing for months and used blockchain analysis tools provided by Chainalysis. It marks the largest-ever freeze of a stablecoin, a press release said.

On-chain data shows that Tether froze the $225 million across 37 wallets, with the majority of those tokens previously being transferred to OKX, a crypto exchange that also took part in the investigation.

The crime syndicate is related to the "pig butchering" scam, which the Federal Bureau of Investigation (FBI) said cost U.S. citizens $3.3 billion last year.

The frozen tokens were being held in self-custodied wallets and did not belong to Tether customers, the press release added.

"Through proactive engagement with global law enforcement agencies and our commitment to transparency, Tether aims to set a new standard for safety within the crypto space,” said Paolo Ardoino, CEO of Tether.

Tether also froze 32 crypto addresses linked to terrorism and warfare in Ukraine and Israel last month.

UPDATE (Nov. 20, 15:15 UTC): Adds paragraph linking to on-chain data.