Senators tell Geithner not to ease Iran sanctions law

WASHINGTON (Reuters) - Senators on Thursday warned Treasury Secretary Timothy Geithner not to weaken a new law aimed at thwarting Iran's nuclear ambitions by allowing countries to use different criteria to escape financial sanctions.

The Treasury is grappling with how to implement the law that prohibits countries and their institutions from dealing with Iran's central bank, the main conduit for Tehran's oil revenues.

How the Obama administration defines whether a country has "significantly reduced" its crude oil purchases from Iran will determine whether that country will be cut off from the U.S. financial system.

"An unevenly applied interpretation would ... call into question the seriousness of the sanctions policy and send mixed signals to both Iran and our allies," senators Mark Kirk and Robert Menendez said in a letter to Geithner.

Kirk, a Republican and Menendez, a Democrat, jointly crafted the original Iranian measure. They asked Geithner to use prices instead of volume of oil to define the law and said at a minimum governments should pay Iran 18 percent less for its oil to be in compliance with the U.S. law.

"A successful sanctions policy will be judged by its impact on the Iranian bottom line, driving its net oil revenues down regardless of its actual supply of oil to the market," the senators said.

The Obama administration, however, is focused on making countries cut their purchases of Iran oil and believes it is getting enough indications that countries will be reducing their oil imports.

The Treasury Department could not be immediately reached for comment.

(Reporting By Rachelle Younglai; Editing by Eric Walsh)