Washington, Jan. 9 -- US Republican Senator Lindsey Graham has issued a sharp warning to Iran's Supreme Leader Ayatollah Ali Khamenei, saying President Donald Trump could resort to lethal action if the Iranian authorities continue to kill or injure protesters.

He also said that Khamenei was a "religious Nazi who kills his own people and terrorises the world".

Graham made the remarks during a Tuesday night appearance on Fox News, referring to the ongoing anti-regime protests sweeping across Iran that erupted after a sharp decline in the value of the Iranian rial against the US dollar.

Demonstrations that began on December 28 quickly spread to several cities and towns, with some turning violent and leading to clashes with security forces...