Iran would have no alternative but to acquire a nuclear weapon if attacked by the United States or its allies, an adviser to the country's supreme leader warned on Monday, following a threat by Donald Trump.

Iran's Supreme Leader Ayatollah Ali Khamenei said the U.S. would receive a strong blow if it acts on President Donald Trump's threat to bomb unless Tehran reaches a new nuclear deal with Washington.

Iran’s president says Tehran had rejected direct negotiations with the United States in response to a letter from President Donald Trump over its rapidly advancing nuclear program.

Iran and Russia took decisively different approaches in response to President Donald Trump's threats as Tehran vowed action against any "mischief" while the Kremlin remains tight-lipped.