June 25 (UPI) — A cargo vessel in the Strait of Hormuz was attacked Thursday, prompting officials to halt the evacuation of sailors stranded in the chokepoint by the war.

It was unclear who attacked the cargo ship. According to the British navy’s United Kingdom Maritime Trade Operations office, the vessel was struck on its starboard side by an unknown projectile at about 5:40 p.m. local time. It was about 7 1/2 nautical miles southeast of Dahit, Oman, when it was attacked, it said.

The vessel’s bridge sustained damage, but no casualties or environmental impact were reported.

Following the attack, the United Nations’ International Maritime Organization paused its evacuation operation in the Strait of Hormuz.

“I have decided to temporarily pause its implementation in order to reconfirm that the necessary safety guarantees continue to be in place for the ships on our evacuation list and all those in the region,” IMO Secretary-General Arsenio Dominguez said in a statement.

The war, which began Feb. 28, left some 11,000 sailors stranded in and around the Strait of Hormuz, a vital energy shipping route. The IMO announced the evacuation operation Tuesday, after the United States and Iran agreed to a Memorandum of Understanding that seeks to pave a path to ending the war.

Under the U.N. plan, a number of vessels have already been evacuated.

The vessel struck Thursday was not transiting the Hormuz under the IMO’s evacuation framework, the U.N. agency said.

Though it unclear who was responsible for the attack, the Iran’s U.S.-sanctioned Persian Gulf Strait Authority, newly created by Tehran to oversee and manage the strait, issued an advisory Thursday, stating it is not responsible for the protection of vessels transiting “outside designated routes.”

“Any consequences arising from unauthorized routing shall be the sole responsibility of the vessel owner, charterer and master,” it said.

Control of the strait has been a focus of ongoing U.S. efforts to end the war.

Iran effectively closed the strait after being attacked Feb. 28, causing energy prices to surge and threatened nations with worsening energy crises.

Since then, Iran has attempted to maintain control of the strait and has sought to impose fees on ships that transit it.

The United States is seeking to secure free maritime travel through the strait as part of the MOU. U.S. Secretary of State Marco Rubio is currently in the Middle East trying to sell the MOU to allied nations.

However, the Institute for the Study of War said in a report Thursday night that Iran’s alleged attacks and threats directed at vessels in the strait “advance its objective of establishing control over the waterway” as well as “undermine international efforts to guarantee safe passage through the Strait of Hormuz.”

“Iran is using military threats and economic incentives to try to convince Gulf states to support its efforts to control the strait, but the Gulf states appear to be resisting Iranian pressure at present,” it said.