India, Feb. 2 -- After Iran's Supreme Leader Ayatollah Ali Khamenei warned the United States that any attack on the country would spark a "regional war" in the Middle East, US President Donald Trump said that if Tehran does not make a deal with Washington, then he'll find out whether the Iranian leader was right about his caution.

Khamenei's warning to Trump came amid the increasing strain in Iran's ties with the US. The Supreme Leader visited the shrine of Ruhollah Khomeini, the Islamic Republic's founder, in southern Tehran, in a rare public appearance on Saturday. Follow live updates on Iran-US tensions

A day later, he responded to Trump's threats of a military strike and said there would be a "regional war" in the Middle East in cas...