April 13 (UPI) — The U.S. military said it will begin blocking all ships from leaving or entering Iran’s ports on Monday morning in line with a maritime blockade ordered by U.S. President Donald Trump to cut off Iranian oil exports.

U.S. Central Command said in a news release Sunday that the blockade would be enforced equitably against vessels of all nations sailing to or from Iranian ports, including all those on the Persian Gulf and Gulf of Oman, but stressed vessels serving ports in neighboring countries would be left alone.

“CENTCOM forces will not impede freedom of navigation for vessels transiting the Strait of Hormuz to and from non-Iranian ports,” said the news release, which instructs the masters of all ships to monitor “Notice to Mariners” broadcasts and make radio contact with U.S. naval forces on bridge-to-bridge channels in Gulf of Oman and Strait of Hormuz approaches.

The blockade would effectively cut off Iran’s international trade by preventing it from importing or exporting anything by sea, in particular its energy exports on which it is reliant for hard currency.

Further details would be communicated in a formal notice that would be provided to commercial ships and operators prior to the start of the blockade, due to come into force at 10 a.m. EDT, CENTCOM said.

The statement clarified comments by Trump early Sunday in which he appeared to announce a total blockade of the Strait of Hormuz in response to the failure of peace talks in Pakistan at the weekend.

Trump had said the U.S. Navy “will begin the process of BLOCKADING any and all Ships trying to enter, or leave, the Strait of Hormuz.”

On Saturday, CENTCOM announced that the U.S. Navy guided-missile destroyers USS Frank E. Peterson USS Michael Murphy had transited the Strait of Hormuz and operated in the Persian Gulf, preparatory to clearing Iranian mines and reopening the shipping route to commercial vessels.

Tehran responded to the development with unspecified threats against the ports of its neighbors and raised the specter of widening the conflict to the Red Sea, the other sea passage in the region that is critical to the global economy.

“Security in the Persian Gulf and the Sea of Oman is either for everyone or for NO ONE. If Iran’s ports are threatened, NO PORT in the region will be safe,” the Iranian military’s central command said in a statement carried by state-run broadcaster IRIB.

“Naval blockade of Iran? Bab al-mandeb Coming soon?!,” IRIB said earlier in a post referencing the narrow strait at the southern entrance to the Red Sea, which leads to the Suez Canal, where Iran-backed Houthi rebels attacked around 100 commercial ships November 2023 through September 2025.

Oil prices rose in response to the developments while stock markets retreated.

The benchmark Brent crude and West Texas Intermediate both climbed back above $100 a barrel with the Brent contract for June delivery changing hands at $102.31 per barrel in mid-morning trade in London while the WTI contract for May was trading at $104.44.

The FTSE 100 in London was down 0.33%, the DAX in Frankfurt fell almost 1.2% and France’s CAC 40 was off by almost 1%.

Former U.S. special envoy to the region David Satterfield expressed concerns over the blockade, warning that if shipping continued to be affected current supply disruption would widen beyond oil, with serious implications for Gulf countries’ exports of many other critical materials from aluminum and helium to polymers and fertilizer feed stocks.

“The Gulf is a critical global supply point, far beyond hydrocarbons — and the impact if this goes on for several more weeks is going to become quite profound, beyond just the cost of petrol and diesel at the pump,” Satterfield told the BBC.