Iran remained defiant over its nuclear programme on Monday as representatives of six major powers prepare to meet in Germany this week to look at ways of persuading it to curb its atomic ambitions.

The unyielding comments from parliament speaker Ali Larijani, a former lead negotiatior on the nuclear issue, came despite overtures from the new US administration of President Barack Obama, who has offered Iran an extended hand of diplomacy if its leaders "unclenched their fist."

"If they (the United States and the international community) want Iran to give up the know-how it has regarding the nuclear programme, they are talking nonsense," Larijani told a news conference.

"This kind of talk has no legal basis and it is against the will of the Iranian public," he said, adding that it was the international community which has to "give up their preconditions" if they want to hold talks with Iran.

In a break with the policy of president George W. Bush, Obama has offered to open a dialogue with Iran without preconditions, something that was strongly welcomed by UN atomic watchdog chief Mohamed ElBaradei in an interview published on Sunday.

"You're not going to have trust unless you have a direct dialogue," ElBaradei told the Washington Post.

"President Obama is saying he's ready to have a direct dialogue without preconditions, based on mutual respect. I say this is absolutely overdue."

But when asked about the change of tack by the Obama administration, Larijani insisted: "We still have not seen any new approach.

"There is still some talk about big sticks and big carrots (regarding Iran's nuclear programme)," he told reporters.

Larijani took particular issue with a recent White House statement making clear that Obama had not ruled out the option of a military strike against Iran.

"Putting the military option on the table was wrong from the start," he said.

"I think Obama made a mistake by saying it. We are not deterred by these things."

Wednesday's meeting of the six major powers in Frankfurt will be the first since Obama took office on January 20.

The six -- Britain, China, France, Germany, Russia and the United States -- have been at loggerheads with Iran over its nuclear work, which Washington and other Western powers suspect of being a cover for a drive to produce the bomb.

The UN Security Council has already adopted four resolutions requiring Iran to suspend its uranium enrichment programme, three of which imposed sanctions.

Iran insists its nuclear programme is for civil energy uses only.

In December, ElBaradei, said international efforts to halt Iranian nuclear activity had been a failure.

The IAEA reported in November that Iran had more than 5,000 uranium enrichment centrifuges in operation.

Larijani confirmed he will attend an international security conference in Munich later this week but ruled out any possibility of talking with US delegates, who are to include Vice President Joe Biden.

The February 6-8 conference is to focus on disarmament, world energy supplies and regional security issues, and Larijani said: "My contribution at the conference will be limited to these topics."

However, former parliament speaker Mehdi Karroubi, a leading reformist who plans to stand in Iran's presidential election in June, said he was in favour of dialogue with Washington.

"The taboo of negotiations with the United States has been broken with the letter of congratulations," the semi-official ILNA news agency quoted him as saying in reference to a surprise letter sent by President Mahmoud Ahmadinejad to Obama after his election victory in November.

"Therefore it is possible to talk with the United States within the framework of foreign policy defined by the supreme leader (Ayatollah Ali Khamenei)," Karroubi said.