WASHINGTON, Aug 8 (Reuters) - The U.S. Treasury told the British government on Wednesday that it takes financial sanctions violations "extremely seriously" and is coordinating with federal and state agencies in an investigation of the UK's Standard Chartered bank.

Adam Szubin, director of Treasury's Office of Foreign Assets Control, told the British Treasury in a letter obtained by Reuters that his office is investigating the bank for "potential Iran-related violations as well as a broader set of potential sanctions violations."

The letter, dated Aug. 8, was in response to a British request for clarification of U.S. sanctions laws and comes after New York State authorities alleged that Standard Chartered hid $250 billion of Iranian banking transactions, in violation of U.S. law.

Szubin told British authorities that in 2008 the Treasury Department outlawed the so-called U-turn transaction license - licenses the New York banking regulator accused Standard Chartered of using to evade sanctions.

The New York State Department of Financial Services order alleged that even as some banks exited the U-turn transactions, Standard Chartered hustled to "take the abandoned market share."

The alleged U-turn transactions refer to money moved for Iranian clients among banks in the United Kingdom and Middle East and cleared through Standard Chartered's New York branch, but which neither started nor ended in Iran.

Although the bulk of Szubin's letter detailed how the license worked prior to 2008, he made clear that his explanation was not a comment on the New York State regulator's order.

Szubin said his office will continue to coordinate with relevant U.S. authorities, including the New York regulator, and would have "no public comment on that investigation until its conclusion."