WASHINGTON - A senior U.S. Treasury Department official said on Tuesday that if Iran fails to demonstrate that it is not seeking nuclear weapons it may face sweeping sanctions from the rest of the world.

The plan we are developing is comprehensive, Treasury's under secretary for terrorism and financial intelligence, Stuart Levey, said in prepared testimony for delivery to the Senate banking Committee.

It takes into account that no single sanction is a 'silver bullet' -- we will need to impose measures simultaneously in many different forms in order to be effective.

Levey was not specific and said he could not describe everything that was being planned at a public hearing but said any measures would be taken with international cooperation.

Because financial measures are most effective when imposed as part of a broad-based effort with support of the largest possible international coalition, we are working closely with our allies as we put together this strategy, he said.

Levey said that by targeting key vulnerabilities and fissures in Iran, allies could if necessary show the Iranian government that it would face serious costs for failing to cooperate with the international community.

At talks in Geneva last week between Iran and six major powers including the United States over Tehran's nuclear program, Iran said it would let U.N. inspectors into a newly disclosed uranium enrichment plant.

Levey noted that President Barack Obama had stated that while the Geneva talks were helpful, the United States was not prepared to negotiate indefinitely and was prepared to move toward increased pressure if Iran does not cooperate.

(Reporting by Glenn Somerville; Editing by James Dalgleish)