President Donald Trump said the US will impose an unprecedented level of economic isolation on Iran and warned that third countries trading with or providing economic support to Tehran would also face severe penalties.

Speaking on Aug. 19, Trump said he was announcing “the most powerful economic operation ever undertaken against any country.” He called it an economic war and isolation campaign on an unprecedented scale.

Trump made clear the effort would extend beyond direct sanctions on Iran to pressure third countries as well. Any country providing Iran with “any form of lifeline” through financial institutions, companies, airports or government agencies would pay a tremendous economic price, he said.

He identified oil smuggling, currency swaps, cash transfers, exchange houses, ship registration and shell companies as specific targets. “All of this must stop immediately,” Trump said.

Trump also urged US allies to join the economic blockade on Iran. Describing the move as “Economic D-Day,” he said all allies must stand with the US to isolate and repel the Iranian threat.

He said the measures were prompted by Iran’s refusal to accept a negotiating opportunity offered by the US. “No one gave Iran more of a chance to make a deal than I did,” Trump said. “Unfortunately, Iran failed to seize that opportunity.”

Trump also said Iran’s naval and air forces and its munitions facilities had already suffered major damage, while the country’s currency had plunged. He argued the economic measures would sharply restrict Iran’s ability to conduct further military activity.

Trump ended by saying Iran would never obtain a nuclear weapon.