India, Jan. 13 -- Iran appears to be edging closer to a political upheaval that could redraw the global map.

Night after night, massive crowds have flooded the streets across the country, challenging the authority of Supreme Leader Ayatollah Ali Khamenei in what analysts describe as the most serious threat to the Islamic Republic in decades.

Demonstrations that began two weeks ago have spread rapidly from Tehran to dozens of cities.

Despite threats, internet shutdowns and violent crackdowns, hundreds of thousands of Iranians have reportedly defied security forces, marking an unprecedented wave of resistance in a nation of nearly 90 million people.

The unrest has drawn strong reactions from US President Donald Trump, who recently overs...