White House calls for 'punitive' measures against Iran in nuclear row

The comments came hours before a conference call with senior officials from China, Russia, France, Germany and Britain to decide how to proceed will be held.

The major powers say they fear Tehran wants to build an atomic bomb. But Iran, the world's fourth-largest oil producer, insists it is only seeking to master nuclear technology to generate electricity.

"In the absence of a positive response to the generous offer that we provided for in our extended package, we think that the allies will have no choice but to take further measures that would be punitive," White House spokeswoman Dana Perino said aboard Air Force One.

Going nuclear: Four long and medium range missiles rise into the air after being test-fired at an undisclosed location in the Iranian desert on July 9, 2008

Iran's one-page letter handed to European Union foreign policy chief Javier Solana yesterday gave no firm reply to an offer from the major powers to refrain from more U.N. penalties if Iran freezes expansion of its nuclear work. Iran instead promised a "clear response" at an unspecified date.

"I think that the Iranians have long stalled on responding to the allies, so I think the most important thing we can do is let the political directors have their conference call and decide on their next steps," said Perino, travelling with U.S. President George W. Bush in Asia.

The letter from Tehran said, "Iran is ready to provide a 'clear response' to your proposal at the earliest possibility, while simultaneously expecting to receive your 'clear response' to our questions and ambiguities as well."

Referring to the letter, Perino said, "We don't have the decent and responsive statement from the Iranians."

A spokesman for Germany's foreign minister told a news conference that officials would use the conference call later on Wednesday to jointly analyse and evaluate the letter.

"The German government believes it is important to maintain the unity between the EU3 (Germany, France and Britain) plus 3 (United States, China and Russia) and that this unity is an important recipe for the success of our policy towards Iran."

Tehran has repeatedly refused to halt its atomic work, prompting the U.N. Security Council to impose three rounds of penalties on Iran since 2006. The United States also maintains its own sanctions against Iran.

Diplomats cautioned it would be difficult to pass a fourth round of Security Council sanctions against Iran because of reluctance from Russia and China, as well as Germany.

The major powers have said formal talks on the incentives could only start once Iran suspends uranium enrichment, the part of the program that most worries the West because it has military and civilian uses.

The head of Iran's Revolutionary Guards said this week his country could easily close the Strait of Hormuz, a key Gulf shipping route, if it were attacked over its nuclear programme -- prompting a warning from the United States that such a move would be a "self-defeating exercise".

Israeli cabinet minister Shaul Mofaz, a frontrunner to succeed Prime Minister Ehud Olmert, denounced his native Iran on Wednesday as "the root of all evil" and said its nuclear programme constituted a threat to world peace.

He urged the West to impose stiffer sanctions to pressure Iran to stop its nuclear programme. Israel is widely believed to have assembled the Middle East's only nuclear arsenal.