The United States will unilaterally declare on Saturday that UN sanctions against Iran are once again in force.
"Virtually all UN sanctions on Iran will come back into place this weekend at 8:00 p.m. Eastern Time (midnight GMT) on Saturday the 19th," said Elliott Abrams, the Trump administration's special representative for Iran.
In mid-August, President Donald Trump's administration suffered a resounding defeat at the UN Security Council when it tried to extend the embargo on conventional weapons being sent to Tehran, which was due to expire in October.
Secretary of State Mike Pompeo made an unusually vehement attack on allies France, Britain and Germany, accusing them of "siding with Iran's Ayatollahs," and on August 20 announced a controversial move known as the "snapback," which aims to re-establish all sanctions against Tehran a month later.
The sanctions were lifted in 2015 when Iran signed on to an international agreement not to seek to build nuclear weapons.
But Trump said that the landmark accord, negotiated by his predecessor Barack Obama, was insufficient and withdrew the US from the agreement in 2018, then renewed and even strengthened Washington's bilateral sanctions.
At the moment, the United States is insisting it is still a participant in the agreement that it stormed out of, but only so that it can activate the "snapback" option.
Virtually every other member of the Security Council disputes Washington's ability to execute this legal pirouette, and the council has not taken the measure any further.
The US is, however, demanding that the arms embargo be prolonged "indefinitely," and that numerous other activities linked to Iran's nuclear and ballistic programs be subject to international sanctions.
Pompeo said this week the US will "do all the things we need to do to make sure that those sanctions are enforced.
"We are going to act in a way -- and we have acted in a way -- that will prevent Iran from being able to purchase Chinese tanks and Russian air defense systems," he said
"We expect every nation to comply with UN Security Council resolutions -- period, full stop," he added.