"I think it's over," he said Wednesday in Ankara, sitting next to NATO Secretary-General Mark Rutte at the alliance's annual summit. "As far as I can tell, it's just a waste of time."

Trump's comments came shortly after the US launched a new wave of strikes against Iran and revoked permission for Iranian oil sales. These actions, taken in response to recent attacks on ships in the Strait of Hormuz, have brought new volatility to energy markets and tested the already fragile peace agreement between Washington and Tehran. “I don’t want to deal with them; they’re scum,” Trump said. “You know what scum is? That’s them. They’re sick people, they’re led by sick people, they’re cruel and aggressive, and if they had nuclear weapons, they would use them.”

Three ships were attacked in the Strait of Hormuz, apparently by Iran, which has repeatedly stated it will not allow ships to transit the crucial energy route without its permission. Ending attacks on commercial shipping and allowing the US to do so were central elements of the memorandum of understanding that halted hostilities between the US and Iran and established a 60-day period for negotiations on a broader peace agreement.

Taken together, these events pose the most serious threat yet to the interim peace agreement. The US blamed Iran for the attacks on the ships, while Tehran claimed that the military strikes and the withdrawal of the permit violated the agreement between the countries.

Oil prices, which peaked near $125 per barrel in late April, returned to pre-conflict levels this month amid signs of recovery. But after the US Treasury's decision, prices soared again and are up more than 6% on Wednesday. Brent crude was trading above $78.50 per barrel at the time of writing.