US President Donald Trump has threatened economic penalties against any country whose banks, businesses, airports or government bodies help Iran, in a post on Truth Social on August 19.

The threat extends US secondary sanctions enforcement to third countries at a point when Tehran's remaining commercial channels are closing. It follows the UAE's decision to halt all trade and financial transactions with Iran, cutting a route that supplied more than 30% of Iranian imports, and puts on notice the Chinese refiners that remain the largest buyers of Iranian crude.

Trump said the operation would be the most crushing ever taken against any country. He warned that any state permitting its institutions to provide "any type of lifeline to Iran" would face severe consequences, listing oil smuggling, swap lines, cash transfers, exchange houses, ship registries and front companies.

The announcement builds on a campaign run since April under the name Operation Economic Fury, which has targeted Iranian oil, shipping and banking alongside a naval blockade of Iranian ports.

Washington has already pushed into the intermediary networks Trump named, with Istanbul and Dubai fintechs drawn in when sanctions were imposed on Iran's richest crypto holder, billionaire Babak Zanjani.

In that case, the US Department of the Treasury said on July 24 that its Office of Foreign Assets Control (OFAC) has designated four more individuals and nine entities in countries including Turkey and the UAE for forming key components of the wider Iranian sanctions evasion network of Iranian billionaire business magnate Babak Zanjani.

“The Iranian regime continues to pay a steep economic price for its reckless behavior, with the rial plunging to another record low and inflation up massively,” US Secretary of the Treasury Scott Bessent said in a comment on the development.

The UAE halted trade on August 19 after saying two ballistic missiles fired from Iran fell into its territorial waters, causing no damage. Iranian Foreign Ministry spokesman Esmaeil Baghaei denied that Iran had launched them. Emirati operators had already cut Iranian mobile roaming, disrupting banking access for expatriates while already seizing Iranian bank accounts in the UAE and shutting down Bank Melli offices in Dubai.

Earlier, Trump said on August 18 that no talks were under way or scheduled. A 60-day window for negotiations lapsed without a breakthrough, though Tehran has said there was no 60-day deadline in its Islamabad understanding with Washington.

Chinese Foreign Ministry spokesperson Lin Jian said that sanctions and economic pressure would not help resolve the issue as it continues to trade with Iran and other Gulf nations in a bid to keep its supplies of oil and LNG flowing through the significantly diminished route of the Hormuz.

Following China's comment, Iran said the Hormuz will stay shut until US oil sanctions are lifted. Hours after Trump's post, Tehran said banking barriers with Iraq had been removed.