US does not seek war with Iran: Pompeo

US Secretary of State Michael Pompeo on Tuesday said his country is not seeking war with Iran, despite a spike in tensions that has seen the Pentagon dispatch nuclear-capable bombers to the region.

Iran's supreme leader Ayatollah Ali Khamenei meanwhile insisted the showdown between the Islamic republic and the United States was a test of resolve rather than a military encounter.

"We fundamentally do not seek a war with Iran," Pompeo said during a visit to Russia, a key backer of Tehran which has blamed the current crisis on Washington's decision to pull out of the Iran nuclear deal.

But Pompeo added: "We have also made clear to the Iranians that if American interests are attacked, we will most certainly respond in an appropriate fashion."

"We are looking for Iran to behave like a normal country," Pompeo said, pointing in part to Tehran's backing of Huthi rebels in Yemen who are under attack from US ally Saudi Arabia.

Huthi rebels "are launching missiles into areas where there are Russians and Americans travelling. These missiles could easily kill a Russian or an American," Pompeo said.

Khamenei echoed Pompeo's rhetoric in a speech to officials.

"This face-off is not military because there is not going to be any war. Neither we nor them (the US) seek war. They know it will not be in their interest," he said, quoted on his website.

"The definite decision of the Iranian nation is to resist against America," Khamenei said, adding that "in this showdown America will be forced to retreat... because our resolve is stronger."

The supreme leader said negotiating with the US was "poison" because the Americans wanted to deprive Iran of its missiles and "strategic depth" in the region.

"Negotiating with the present American government is doubly poisonous... they are not decent humans, they don't stand by anything," he said referring to the US decision to withdraw from the landmark 2015 nuclear deal between Iran and major world powers.

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US 'maximum pressure' campaign

Washington last year pulled out of a nuclear deal backed by Europe, Russia and China, which curbed Iran's nuclear ambitions in return for sanctions relief.

Since then it has slapped sweeping sanctions on Iran in an all-out effort to reduce Tehran's regional clout.

The US has recently ramped up the pressure, deploying an aircraft carrier strike group and nuclear-capable bombers to counter vaguely described threats from Iran.

On Sunday, mysterious attacks by unknown assailants against four ships in the region, including two from Saudi Arabia, sent war talk up another notch.

UN inspectors have said Iran is complying with the deal, and Moscow last week denounced new US sanctions on the country's mining industry, calling for new talks to save the nuclear accord.

During Pompeo's visit, Russian Foreign Minister Sergei Lavrov said Moscow would work "to ensure this situation does not descend into a military scenario".

"I hope that reason will triumph," Lavrov said, adding that he hoped reports in the US media that President Donald Trump is planning to send 120,000 troops to counter Iran turn out to be wrong.

Trump himself rejected the New York Times report, saying it was "fake news" but did not rule out deploying "a hell of a lot more" soldiers in the future.

Kremlin spokesperson Dmitry Peskov earlier Tuesday slammed what he called Washington's "maximum pressure" campaign on Iran, saying it would only drive Tehran into a corner.

Pompeo cancelled a stop in Moscow Monday to instead have an unscheduled meeting in Brussels with European foreign ministers, who have been uncomfortable with the hawkish direction of the US on Iran.