Washington/Berlin: President Barack Obama's administration signalled on Thursday that the United States reserved all its options, ranging from diplomacy to military action, to pressure Iran over its nuclear programme.

The 10-day-old administration is reviewing US policy toward Tehran, but in a break with the hard-line stance of former President George W. Bush, who branded Iran part of an "axis of evil", Obama has said he is prepared to pursue direct diplomacy with Iran without preconditions.

"We must use all elements of our national power to protect our interests as it relates to Iran. That includes, as the president talked about in the campaign, diplomacy where possible," Obama's spokesman, Robert Gibbs, said.

"We have many issues to work through - an illicit nuclear programme, the sponsorship of terrorism and the threatening of peace in Israel are just a few of the issues that this president believes the Iranian leadership must address," Gibbs told a White House news conference.

Asked whether Obama's view was that the military option remained on the table, he said, "The president hasn't changed his viewpoint that he should preserve all his options."

Bush always insisted that all options, including military action, remained open in dealing with Iran, though he said he was seeking a diplomatic solution.

Iran is engaged in a stand-off with the West over its uranium enrichment program, which it says is for the peaceful generation of electricity but which Western countries fear is a cover to build an atomic weapon.

During his campaign for the presidency, Obama said he would offer Iran various incentives, including helping it to join the World Trade Organization, if it stopped its nuclear work. But he also threatened to step up economic pressure and deepen Iran's political isolation if it refused.

In his first formal television interview since his election as president, Obama said this week he was prepared to extend a hand of peace to Iran if it "unclenched its fist."

Analysts expect Obama to adopt a cautious approach to Iran ahead of elections there in June. President Mahmoud Ahmadinejad is running for a second four-year term and could face the moderate politician Mohammad Khatami.

One problem facing the Obama administration, if they decide to pursue diplomacy, is who exactly in Tehran to talk to. While Ahmadinejad is president, Iran's top authority is Supreme Leader Ayatollah Ali Khamenei, who said in October that hatred of America ran deep in Iran.

"It's unclear exactly who that dialogue would be with in Iran," Gibbs said. "In order for this to happen, there has to be some preparation and an understanding ... by both sides."