Iran said on Tuesday that the West had no proof it was developing nuclear weapons, as the Islamic Republic braced for a UN report expected to provide new evidence that it is seeking the atomic bomb.

Foreign Minister Ali Akbar Salehi denied the UN atomic watchdog report could undermine Iran's insistence that its nuclear programme is peaceful while President Mahmoud Ahmadinejad declared Tehran did not even need the bomb.

The International Atomic Energy Agency (IAEA) report on the Iranian nuclear programme is being published just after Israel's President Shimon Peres warned that a pre-emptive attack on Iran had become more likely.

"There is no serious proof that Iran is going to create a nuclear warhead," Salehi said, responding to a question about the IAEA report during a visit to neighbouring Armenia.

"The West and the United States are exerting pressure on Iran without serious arguments and proof," he said.

The IAEA report, thought to be set for release Wednesday, is said by diplomats in Vienna to be the watchdog's harshest report yet against Iran's nuclear programme.

It is to contain evidence of activities suggesting work that could be used for developing nuclear warheads and ballistic missiles, though stopping just short of definitively saying that is the case, diplomats said.

Previous IAEA assessments have centred on Iran's efforts to produce fissile material -- uranium and plutonium -- which can be put to peaceful uses such as power generation or be used to make a nuclear bomb.

In typically defiant style, Ahmadinejad said his country "does not need an atomic bomb" and would instead "act thoughtfully" to confront US threats against it, according to state media.

However he warned: "If America wants to confront the Iranian nation, it will certainly regret the Iranian nation's response."

Peres warned on Sunday that a strike against Iran was becoming more likely, in one of the starkest warnings by the Jewish state to Tehran in recent times.

"The possibility of a military attack against Iran is now closer to being applied than the application of a diplomatic option," Peres said.

Avigdor Lieberman, the hawkish foreign minister of Israel, said only "crippling sanctions" would be able to thwart Iran, the Maariv newspaper reported.

Iranian Defence Minister Ahmad Vahidi shrugged off Peres' warning, saying the reports were just "media clamour" and the Islamic republic was able to face down any threat.

"We have repeatedly said that our country's defensive capability, whether at sea, by missile, or underwater, is very high and up-to-date and we have the might to fend off any threats," the ISNA news agency quoted Vahidi as saying.

But President Dmitry Medvedev of Russia -- which has a history of close ties with the Islamic Republic -- said that Israeli threats were "extremely dangerous rhetoric" that could result in a "catastrophe".

"All this could lead to a very big conflict and that would be a catastrophe for the Middle East," he told reporters on a visit to Berlin.

Salehi repeated Tehran's position that its nuclear programme was for peaceful purposes only.

"We have repeatedly stated that we are not going to create nuclear weapons," he said. "Our position has always been that we will never use our nuclear programme for purposes other than peaceful ones."

The United States -- which last month accused Iranian officials of masterminding a thwarted plot to assassinate the Saudi ambassador to Washington -- is keen to use the report to build world support for more sanctions on Iran.

"We certainly expect it to echo and reinforce what we've been saying about Iran's behaviour and its failure to live up to its international obligations," said White House spokesman Jay Carney.

Germany's foreign ministry called for "greater political and diplomatic pressure" on Iran while French Foreign Minister Alain Juppe said sanctions should be toughened but "everything must be done" to avoid a military conflict.

Iran nuclear crisis timeline
Tehran (AFP) Nov 8, 2011 - Key developments in the standoff over Iran's nuclear programme:

2005

- Aug 8: Iran resumes uranium conversion activities which had been suspended since November 2004.

2006

- April 11: Iran says it has enriched its first uranium to 3.5 percent purity and later, in May, to 4.8 percent. This is insufficient to make a nuclear bomb.

- Dec 23: The UN Security Council imposes sanctions on Iran's trade in sensitive nuclear materials and technology. It strengthens the measures in 2007, 2008 and 2010.

2007

- April 9: President Mahmoud Ahmadinejad says Iran can produce nuclear fuel on an industrial scale.

2009

- April 9: Iran inaugurates its first nuclear fuel plant, and says it has installed 7,000 uranium enrichment centrifuges at Natanz.

- Sept 25-28: Iran reveals a secret uranium enrichment plant, Fordo, which is being built inside a mountain near the holy city of Qom.

- Oct 21: The International Atomic Energy Agency floats a plan under which Iran's nuclear fuel would be enriched outside the country; Tehran rejects the offer.

2010

- June-July: World powers enact new military and financial sanctions.

- July 30: Iran says it is ready for immediate talks with the United States, Russia and France over an exchange of nuclear fuel.

- Aug 16: Iran announces it is to start building its third uranium enrichment plant in early 2011.

- Aug 21: Iran starts loading fuel into its Russian-built first nuclear plant at Bushehr.

- Nov 29: Twin blasts in Iran's capital kill a top nuclear scientist and injure another. Ahmadinejad blames Israel and the West.

- Dec 6: After a 14-month break, Iran and six world powers open two days of talks that yield agreement on holding another round of discussions.

2011

- Jan 22: Failure of new talks between Tehran and world powers in Istanbul.

- May 23-24: The European Union and US announce new sanctions against Iran.

- July 19: Iran says it has begun installing new centrifuges with better quality and speed.

- Aug 22: Iran says it has begun transferring centrifuges from Natanz to the Fordo underground site.

- Sept 2: The IAEA says it is getting worried about a possible military dimension to Iran's nuclear activities. It says since February 2007, Iran has produced more than 4,500 kilos (9,920 pounds) of 3.5-percent enriched uranium at its Natanz site.

- Sept 22: Ahmadinejad says Iran will halt production of low-enriched uranium, if the West gives it the material in return. Washington dismisses the proposal.

- Nov 6: Israeli President Shimon Peres warns an attack on Iran is becoming increasingly likely.

- Nov 8: The IAEA has "serious concerns" about Iran's nuclear activities, and has "credible" information Tehran may have worked on developing atomic weapons, a report says.