TOKYO (AP) — A senior U.S. Treasury official has urged banks and financial regulators to do more to tighten oversight of trading in bitcoin and other cryptocurrencies.

Sigal Mandelker, the Treasury undersecretary for terrorism and financial intelligence, said Friday that more needs to be done to prevent money laundering and other criminal activities using such transactions.

Speaking to reporters in Tokyo after visiting China, Hong Kong and South Korea, she lauded recent moves to keep closer tabs on such dealings.

The U.S. considers traders and administrators of cryptocurrencies as "money transmitters" who are required to have strong anti-money laundering and other controls to prevent their use for illegal purposes. It has imposed fines for violations of those regulations.

Financial regulators in Asia have struggled to keep up a boom in crypto currency investing.