WASHINGTON (AP) — The U.S. military stopped a merchant vessel trying to break through its blockade of Iranian ports by firing a missile into its engine room, the U.S. Central Command said on Saturday.

The Gambia-flagged cargo ship Lian Star ignored more than 20 warnings from U.S. forces overnight as it tried to enter an Iranian port, the military said. The ship remained adrift in the Gulf of Oman and U.S. forces have not boarded it, said a U.S. official with knowledge of the situation, speaking on condition of anonymity to discuss military operations.

With the latest action, U.S. military has stopped six ships trying to breach the blockade. One was allowed to proceed. Another 116 ships have been redirected, the military said.

The U.S. launched the blockade on April 17 in response to Iran effectively closing the strait after the war in the Middle East began with U.S. and Israeli strikes on Feb. 28. A fragile ceasefire has held since April 7. Now the region awaits word on whether a deal can be reached to extend it by 60 days while talks would be held on Iran’s disputed nuclear program.

Events in the Strait of Hormuz, a key waterway between Iran and Oman, have shaken the global economy. Shipments of significant amounts of oil, natural gas and related supplies like fertilizer are largely stranded, increasing the strain on consumers and food producers.

The U.S. blockade seeks to limit Iran’s own shipments and further weaken its access to cash, creating more pain for its long-weakened economy.

U.S. President Donald Trump met with advisers on Friday but has yet to decide on whether to move ahead with a deal to extend the ceasefire and reopen the strait. Iran has said the deal had not been finalized.

Commercial traffic has quietly continued to flow through the strait, despite Iran’s assertions that it must approve any transits, though at a much lower volume than before the war.

“Any violation of these regulations will place the security of their passage at serious risk,” Iran’s joint military command said Saturday in a statement carried by state TV, warning that any military vessels trying to interfere with that would be targeted.

Iran has even charged tolls for transit as high as $2 million, which experts have called a violation of a principle of international maritime trade: freedom of peaceful navigation.

Qatar’s deputy prime minister, Sheikh Saoud bin Abdulrahman bin Hassan bin Ali Al Thani, said on Saturday said that the Gulf nation opposes charging fees to transit, “but for certain times when they say they are going to use it for mine clearing or some usage of the fees for a temporary time, this is something that is negotiable, and it could be something that will help the transit of the Strait of Hormuz to be back to normal stage.”

The U.S. official previously told The Associated Press that the U.S. has not found or destroyed any mines in the strait.