A ship in the Strait of Hormuz was attacked, maritime officials said on Tuesday, as a declining number of vessels brave the dangerous passageway.

An unidentified vessel was struck by “an unknown projectile” as it exited the Persian Gulf via Omani waters in the strait, claiming a “crew casualty,” according to the United Kingdom Maritime Trade Operations agency. The agency reported that the engine room was damaged and that the remaining crew members were being assisted by the Omani Coast Guard. Iran has not commented on the attack.

As the conflict between Iran and the United States stretches into its sixth month, traffic in the vital waterway, through which one-fifth of the world’s oil and gas supplies moved before the war began, has dwindled. The average number of ships transiting the strait over the last week was about 12 vessels per day, down from more than 130 a day before the United States and Israel attacked Iran in late February. Many ships travel with their navigation devices turned off to evade attack, making them harder to track.

The war has left hundreds of ships stranded in the Persian Gulf and left commercial sailors on the front lines. Since the war with Iran began, at least 17 sailors have been killed in 65 attacks around the strait, according to the International Maritime Organization, a U.N. agency. Most of the deaths have been the result of Iranian strikes, but three mariners died after the U.S. Navy struck a ship in June.

As uncertainty persists in the Middle East, energy prices have remained elevated. The national average price of gasoline in the United States have been at their highest recorded levels for the month of August, according to the AAA motor club. Brent, the global oil benchmark, was at about $91 a barrel, up from $72 just before the start of the war.

Any resolution between the United States and Iran is likely to include not just an end to a U.S. blockade on Iranian exports, but also a U.S. acknowledgment of Iran’s influence in the Strait of Hormuz, according to a note from Eurasia Group. Iran stands to gain financially if it secures the right to levy fees on ships, but these gains are likely to be eroded over the coming years as Gulf producers invest in pipelines that bypass the strait. Because of this, the significance of the Strait of Hormuz for oil trade may be cut in half by 2030, according to Eurasia Group.

The United States has struck thousands of targets in Iran and dealt blows to the country’s military capabilities, but it has struggled to achieve the war’s political objectives. President Trump’s options in Iran appear to be narrowing, as attempts to negotiate a cease-fire have faltered. On Monday, he lashed out at Oman, a U.S. ally that has been mediating the talks, as efforts to end a war he started have faltered.