India, July 17 -- Tehran has told Yemen's Houthi rebels to be ready to close the Bab al-Mandab Strait if the US strikes Iranian power infrastructure - a warning that comes as hostilities escalated in the Gulf this week, bringing commercial shipping through the Hormuz waterway down to a trickle once again.

The signal, if acted on, would open a second front in a war that has already disrupted about a fifth of the world's oil shipments and pushed Brent crude to around $85 a barrel, up roughly 12% this week. It would draw the Houthis directly into the US-Iran confrontation, and place two of the world's most heavily used maritime chokepoints simultaneously off-limits to global trade.

US President Donald Trump has repeatedly threatened to hit...