China said on Tuesday that a US blockade around Iranian ports was "dangerous and irresponsible", after US President Donald Trump threatened to sink any boats that sought to leave or dock there.

Trump had ordered the blockade of ships entering or leaving Iranian ports and coastal areas in the Gulf following the failure of peace talks over the weekend.

The blockade came into force on Monday despite the United States and Iran agreeing to a two-week ceasefire days earlier.

"The US increased military deployments and took a targeted blockade action, which will only exacerbate tensions and undermine the already fragile ceasefire agreement and further jeopardise safety of passage through the Strait (of Hormuz)," Foreign Ministry spokesman Guo Jiakun said at a news conference.

"This is dangerous and irresponsible behaviour," he added.

Iran had already closed the vital Strait of Hormuz to what it regards as enemy shipping, allowing only vessels serving countries it deems friendly – such as China – to cross.

Trump's blockade, analysts say, aims to starve Iran of funds and pressure Beijing, the biggest buyer of Iranian oil, to lean Tehran to open the strait, through which one fifth of global oil transits.

Tehran's ambassador to the United Nations called Trump's blockade a "grave violation" of Iran's sovereignty. (AFP)



Edited by Thomas McAlinden