Trump says he could be Iran's 'best friend' if it renounces nuclear arms

President Donald Trump said on Saturday that military action against Iran was still an option for its downing of an unmanned US military aircraft, but amid heightened tensions he dangled the prospect of eventually becoming an unlikely "best friend" of Tehran.

Trump also said "we very much appreciate" that Iran's Revolutionary Guard chose not to target a US spy plane carrying more than 30 people.

The president's softer tone on Saturday marked a stark contrast to the anti-Iran rhetoric he employed throughout the presidential campaign and presidency, including his use of punishing economic sanctions in an attempt to pressure Iran to give up its quest to build nuclear weapons.

"The fact is we're not going to have Iran have a nuclear weapon," he said as he left the White House for a weekend at the Camp David presidential retreat. 

"And when they agree to that, they are going to have a wealthy country, they're going to be so happy and I’m going to be their best friend."

"I hope that happens. I hope that happens, but it may not," Trump said.

He later said Iran will be hit with unspecified new sanctions on Monday.

Meanwhile in Tehran, Iranian lawmakers chanted "Death to America" in a parliament session on Sunday, after a speaker accused the US of being the "real world terrorist".

Iran said on Saturday it would respond firmly to any threat against it.

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