WASHINGTON (AFP) - The US Treasury on Tuesday slapped sanctions on the Kodo-kai, calling it the most violent arm of Japan's powerful Yamaguchi-gumi Yakuza crime syndicate.

The sanctions, under laws targeting transnational criminal organisations, were also applied to Teruaki Takeuchi, the chairman of the Nagoya-based, financially powerful Kodo-kai, whose 4,000 members are allegedly involved in extortion and bribery.

The Treasury said Takeuchi was promoted to Kodo-kai head in 2013 by Yamaguchi-gumi deputy godfather Kiyoshi Takayama, the former Kodo-kai chairman who is already on the Treasury sanctions blacklist.

"Takeuchi is also linked to the Inagawa-kai syndicate, the third largest Yakuza syndicate in Japan, through a symbolic brotherhood he shares with Kazuo Uchibori, the second-in-command of the Inagawa-kai," it said.

The sanctions forbid Americans from transactions with those blacklisted, and freeze any assets they have in the United States.

"Today's action builds upon our efforts to undermine the Yakuza financially and disrupt their transnational criminal activities," said John Smith, the acting director of the Treasury's Office of Foreign Assets Control.

"We will continue to target and expose members of criminal organizations like the Yakuza as we work to protect the US financial system from their illicit activity," he said in a statement.

The Treasury has already blacklisted five Yakuza entities as transnational criminal organizations.

Beside their activities inside Japan, Yakuza organized groups have relations with other crime syndicates across Asia, Europe and the Americas, and are involved in drugs and money laundering in the United States, it said.