Tensions escalated Sunday as Iran warned that any military vessels entering the Strait of Hormuz would be treated as a breach of the cease-fire and met with a “strong and forceful response,” following President Trump’s announcement of a blockade targeting the strategic waterway.

Earlier in the day, Trump said the United States would prevent “any and all Ships trying to enter, or leave” the Strait until conditions are met that ensure oil can move freely without interference from Iran.

In response, Iran’s Islamic Revolutionary Guard Corps Navy pushed back, asserting that it maintains complete authority over the Strait and that civilian maritime traffic continues uninterrupted.

“Contrary to the false claims of certain enemy officials, the Strait of Hormuz is open for the passage of non-military vessels under smart control and management, in accordance with specific regulations,” the naval forces said in a statement, according to two semi-official Iranian news agencies.

At the same time, the IRGC warned that any movement by military ships into the area would be viewed as a violation of the cease-fire agreement.

Trump has maintained that last week’s cease-fire arrangement included Iran’s agreement to allow the Strait—through which more than 20 percent of global seaborne oil passes each year—to remain open.

However, Iran has faced accusations of attempting to impose fees on ships passing through the Strait and has also claimed it lost track of naval mines it had deployed, raising concerns among shipping operators and discouraging transit through the already volatile route.

Despite Tehran’s warnings, U.S. officials said two American Navy destroyers passed through the Strait yesterday and successfully shot down an Iranian drone during the transit.