Analysts warn Washington’s blockade could harm the fragile ceasefire between the US and Iran.

United States President Donald Trump’s blockade of the Strait of Hormuz after talks in Islamabad between Washington and Tehran ended without a deal is a substantial escalation in the war on Iran, analysts say.

In a social media post on Sunday, Trump said the US Navy “will begin the process of BLOCKADING any and all Ships trying to enter, or leave, the Strait of Hormuz”.

The blockade began at 10am Washington, DC, time (14:00 GMT) on Monday.

Trump’s comments have raised concerns about the status of the two-week ceasefire between the US and Iran announced last week.

Chris Featherstone, a political scientist at the University of York, told Al Jazeera that Trump’s threat to blockade the Strait of Hormuz is “absolutely an escalation” in the US and Israel’s war on Iran.

“Trump is using the threat of the blockade as a tool in the negotiations with Iran. Trump has said Iran holds no cards, and this attempt to leverage a blockade on Iran would constitute an attempt to further pressure Iran to comply with US goals in the negotiations,” he said.

What could the blockade look like? Here’s what we know:

Shortly after the US and Israel began strikes on Iran on February 28, Iran essentially took control of the Strait of Hormuz, a vital chokepoint for the global energy market. Before the war began, 20 percent of the world’s oil and liquefied natural gas (LNG) supplies were shipped through the strait.

After the Pakistan-brokered ceasefire came into force on Wednesday, Tehran confirmed it would allow shipping through the Strait of Hormuz for the duration of the two-week agreement, easing a disruption that had sent global oil and gas prices soaring.