U.S. President Donald Trump said the United States is in firm control of the Strait of Hormuz, describing the blockade as a “wall of steel” and warning Iran against further attacks.

Axar.az reports that Trump made the remarks to Fox News’ Alexis McAdams ahead of his speech in Nassau County, New York.

“We totally control, we own, in the true sense, we own the Strait of Hormuz,” he said. “We only allow boats to come in if we want them to come in.”

Trump said the blockade is costing Tehran “hundreds of millions of dollars every single day” and argued sweeping U.S. sanctions are also squeezing the regime.

“If they hit, we would hit back 100 times harder,” Trump warned.