Taken from CNBC’s Daily Open, our international markets newsletter — Subscribe today

Hello, this is Leonie Kidd writing to you from London. Welcome to another edition of CNBC’s Daily Open.

I don’t know about you, but I have found that ultimatums rarely work. But President Donald Trump’s decision to issues Tehran with a deadline (which runs until 19:55 eastern time tonight) to reopen the Strait of Hormuz could mark a turning point in the conflict. Good or bad.

The markets don’t quite know what to make of it, with certain stocks markets selling off, while oil surged before turning negative.

U.S. President Donald Trump on Saturday delivered a stark ultimatum to Iran, threatening to “obliterate” Iran’s power plants if Tehran does not fully reopen the Strait of Hormuz within 48 hours.