Iran's supreme leader has banned holding "any talks" with the US following Donald Trump's offer of unconditional dialogue in a bid to improve bilateral ties.

Ayatollah Ali Khamenei, who has the final say on policy in the Islamic Republic, said Mr Trump's reneging of the Obama-era nuclear deal was evidence America cannot be trusted.

He also accused the Iranian government of economic mismanagement in the face to new US sanctions.

Washington reimposed sanctions last week after pulling out of the 2015 international deal aimed at curbing Iran's nuclear programme in return for an easing of economic sanctions.

Mr Trump has also threatened to penalise companies, including ones from the EU, that continue to operate in Iran.

Woody Johnson, the American ambassador to the UK, urged the British government to rethink its support for the "flawed 2015 deal” in a recent article in the Sunday Telegraph.

"I ban holding any talks with America... America never remains loyal to its promises in talks," state TV quoted Mr Khamenei as telling a gathering attended by thousands of Iranians. "America's withdrawal from the nuclear deal is a clear proof that America cannot be trusted."

Trump says he would meet with Iran's leaders without preconditions

The sanctions target Iran's trade in gold and other precious metals, its purchases of US dollars and its car industry.

Washington had said Iran's only chance of avoiding the sanctions would be to accept Mr Trump's offer to negotiate for a tougher nuclear deal. Iranian officials already rejected the offer but it is the first time Mr Khamenei has publicly commented.

However, Mr Khamenei ruled out the possibility of war with the US.

"They (the Americans) are exaggerating the possibility of a war with Iran. There will be no war... We have never started a war and they will not confront Iran militarily," he said.

Mr Khamenei, whose remarks on Monday come amid a sharp fall in the rial currency that has prompted angry protests, criticised the government of president Hassan Rouhani, a pragmatist cleric who championed the 2015 deal aimed at ending Iran's political and economic isolation.

"More than the sanctions, economic mismanagement (by the government) is putting pressure on ordinary Iranians... I do not call it betrayal but a huge mistake in management," state TV quoted Mr Khamenei as saying.

"With better management and more efficient planning we can resist the sanctions and overcome them," Mr Khamenei said, in an apparent effort to deflect public anger over the deteriorating economy towards Mr Rouhani's government.

European countries, which still back the 2015 deal, fear Mr Trump's moves will undermine Mr Rouhani and strengthen the hand of his hardline rivals in the clerical establishment.

Iran parliament reacts after Trump's withdrawal from nuclear deal Show all 10 1 /10 Iran parliament reacts after Trump's withdrawal from nuclear deal Iran parliament reacts after Trump's withdrawal from nuclear deal Iranian MPs burnt a US flag in parliament after Donald Trump announced America's withdrawal from the nuclear deal. AFP/Islamic Consultative Assembly News Agency Iran parliament reacts after Trump's withdrawal from nuclear deal US President Donald Trump displays a presidential memorandum after announcing his intent to withdraw from the JCPOA Iran nuclear agreement in the Diplomatic Room at the White House. Reuters Iran parliament reacts after Trump's withdrawal from nuclear deal Some Iranian MPs reacted after Trumps decision by shouting 'death to America'. AFP/Islamic Consultative Assembly News Agency Iran parliament reacts after Trump's withdrawal from nuclear deal Iranian lawmakers prepare to burn two pieces of papers representing the US flag and the nuclear deal. AP Iran parliament reacts after Trump's withdrawal from nuclear deal Iran said it will hold talks with signatories to the nuclear deal after Trump's decision to withdraw from the accord, which it branded "psychological warfare". AFP/Islamic Consultative Assembly News Agency Iran parliament reacts after Trump's withdrawal from nuclear deal Several Iranian MPs stood chanting in the Tehran parliament. AFP/Islamic Consultative Assembly News Agency Iran parliament reacts after Trump's withdrawal from nuclear deal Iranian MPs burning a US flag AFP/Islamic Consultative Assembly News Agency Iran parliament reacts after Trump's withdrawal from nuclear deal President Hassan Rouhani addressed the nation in a televised speech in Tehran. He said he'd send his foreign minister to negotiate with countries remaining in the nuclear deal after Trump's decision to pull America from the deal, warning he otherwise would restart enriching uranium "in the next weeks." Iranian Presidency Office via AP Iran parliament reacts after Trump's withdrawal from nuclear deal Iran's press condemned Trump's withdrawal from a multi-party nuclear deal but was divided over whether Tehran should react with patience or withdraw itself. AFP Iran parliament reacts after Trump's withdrawal from nuclear deal Trump announced the US withdrawal from what he called the "defective" multinational nuclear deal with Iran, and said Washington would reinstate sanctions against the Islamic republic. AFP/Getty

The rial has lost about half of its value since April in anticipation of the renewed US sanctions, driven mainly by heavy demand for dollars among ordinary Iranians trying to protect their savings.

Iranian officials have blamed "enemies" for the fall of the currency and a rapid rise in the price of gold coins, and more than 60 people, including several officials, have been arrested on charges that carry the death penalty.

"The corrupt people (officials) should be punished firmly," Mr Khamenei said on Monday.

Thousands of Iranians have protested in recent weeks against sharp rises in the prices of some food items, a lack of jobs and state corruption. The protests over the cost of living have often turned into anti-government rallies.

Defying US demands to curb its missile programme, Iran unveiled a new generation of its "Fateh Mobin" short-range ballistic missile on Monday, state TV reported.

"Our will to enhance our defence power in all fields will increase if the pressure mounts on Iran," defence minister brigadier general Amir Hatami said after unveiling the "fully home-made precision-guided" missile.

Mr Trump has said Iran must also stop meddling in conflicts in Syria and Yemen, but foreign minister Javad Zarif struck a defiant tone on Monday, telling Qatar's al Jazeera TV: "Iran will not change its policies in the region because of US sanctions and threats."