Washington: US National Security Adviser John Bolton has warned Iran that here would be “hell to pay” if it continued to “cross” the US and its allies.

Bolton’s comments came hours after President Donald Trump slammed Iran of sowing “chaos, death and destruction” across the Middle East.

The threat was delivered by the national security adviser, John Bolton, a longtime Iran hawk who told an audience of anti-Tehran activists: “The murderous regime and its supporters will face significant consequences if they do not change their behaviour”.

“Let my message today be clear: we are watching, and we will come after you,” Bolton said, according to early excerpts from his speech obtained by the Axios news website.

He added: “If you cross us, our allies, or our partners; if you harm our citizens; if you continue to lie, cheat, and deceive, yes, there will indeed be hell to pay.”

The bellicose tone was in striking contrast to an early morning tweet from Donald Trump saying he was sure that the Iranian president was an “absolutely lovely man”.