The lost mines have prevented Iran from quickly complying with President Trump’s demand to allow more ships to pass through the waterway.

Cargo ships near the Strait of Hormuz, as seen last month from northern Ras al-Khaimah in the United Arab Emirates

Iran has been unable to open the Strait of Hormuz to more shipping traffic because it cannot locate all of the mines it laid in the waterway and lacks the capability to remove them, according to U.S. officials.

The development is one reason Iran has not been able to quickly comply with the Trump administration’s admonitions to let more traffic pass through the strait. It is also potentially a complicating factor as Iranian negotiators and a U.S. delegation led by Vice President JD Vance meet in Pakistan this weekend for peace talks.

Iran used small boats to mine the strait last month, soon after the United States and Israel began their war against the country. The mines, plus the threat of Iranian drone and missile attacks, slowed the number of oil tankers and other vessels passing through the strait to a trickle, driving up energy prices and providing Iran with its best leverage in the war.

Iran left a path through the strait open, allowing ships that pay a toll to pass through.

Iran’s Islamic Revolutionary Guards Corps has issued warnings that ships could collide with sea mines, and semiofficial news organizations have published charts showing safe routes.

Those routes are limited in large part because Iran mined the strait haphazardly, U.S. officials said. It is not clear that Iran recorded where it put every mine. And even when the location was recorded, some mines were placed in a way that allowed them to drift or move, according to the officials.

As with land mines, removing nautical mines is far more difficult than placing them. The U.S. military lacks robust mine removal capabilities, relying on littoral combat ships equipped with mine sweeping capabilities. Iran also does not have the capability of quickly removing mines, even the ones it planted.

In a social media post on Tuesday discussing a pause in the American-Israeli war with Iran, President Trump said a two-week cease-fire was contingent on the “COMPLETE, IMMEDIATE, and SAFE OPENING” of the Strait of Hormuz.

On Wednesday, Abbas Araghchi, the Iranian foreign minister, said that the strait would be open to traffic “with due consideration of technical limitations.” American officials have said Mr. Araghchi’s comment about technical limitations was a reference to Iran’s inability to quickly find or remove the mines.

Mr. Araghchi is now in Islamabad for meetings on Saturday with Mr. Vance. Given Mr. Trump’s demands to open the strait, the issue of how quickly safe passage through the waterway can be increased is likely to be a point of discussion.

The U.S. military sought to destroy Iran’s navy, sinking ships and targeting naval bases. But Iran has hundreds of small boats that it can use to harass ships or lay mines. Destroying all of those small boats has proved impossible.

Even before Iran began laying mines, threats from its leaders quickly disrupted global shipping and sent oil prices up sharply. On March 2, a senior official with the Revolutionary Guards announced that the strait was closed and claimed Iran would set ships “ablaze” if they entered the waterway, according to state media.

In the days after that threat, Iran began mining the strait, even as the United States intensified strikes on Iranian naval assets. At the time, American officials said Iran was not planting mines quickly or efficiently.

Because it was difficult to track the small boats deploying the mines, the United States is uncertain precisely how many Iran has placed in the strait or where they are located.