By Timothy Gardner

WASHINGTON (Reuters) - The U.S. Treasury Department said on Thursday it has imposed sanctions on an Iranian businessman, a Malaysian bank and a network of companies it accused of attempting to evade international sanctions on Iran through money laundering.

The department blacklisted Babak Zanjani, the businessman, and First Islamic Investment Bank for providing financial and other support to the National Iranian Oil Company.

It said Zanjani and a network of companies had moved billions of dollars on behalf of the Iranian government, including tens of millions of dollars to an engineering unit of the Islamic Revolutionary Guard Corps that it uses to earn income.

"As international sanctions have become increasingly stifling, Iran has resorted to criminal money laundering techniques, moving its oil and money under false names and pretenses," said David S. Cohen, under secretary for terrorism and financial intelligence at Treasury.

"Whether through Babak Zanjani ... or tomorrow's chosen accomplice, we will be relentless in exposing and thwarting Iran's attempts to evade international sanctions and abuse the global financial system," he said.

By taking the action against Zanjani, the bank and the network of companies, the department prohibited transactions between them and any U.S. citizen and freezes any assets they have under U.S. jurisdiction, it said.

U.S. and European Union sanctions on Iran's oil industry aim to choke funding for its nuclear program, which they say is being used to develop weapons. Iran says the program is for civilian purposes.

As talks between Iran and major powers have failed to end the deadlock over its nuclear program, lawmakers in the U.S. Senate are preparing legislation that would place further sanctions on Iran.

(Reporting by Timothy Gardner; Editing by Will Dunham and Mohammad Zargham)