Traffic in the Strait of Hormuz has plummeted after Iran’s attack on a Cypriot-flagged container ship on Saturday set off an exchange of strikes with the United States.

Just 14 ships passed through the waterway on Sunday, the lowest level in a month, according to figures from Kpler, a maritime data firm. Of those ships, only three were tankers exiting the Persian Gulf laden with crude oil, chemicals or other commodities, and all three were shadow or sanctioned vessels. Before the start of the war in late February, an average of more than 130 vessels transited the Strait of Hormuz daily.

U.S. forces said they had launched a round of strikes overnight on military targets in Iran. The operation, which used fighter jets, naval vessels, aerial drones and, for the first time, sea drones, aimed to degrade Iran’s ability to attack commercial ships.

With the main shipping route through the strait closed because of a risk of mines, ships are having to choose between navigating through the southern Omani corridor, which is backed by the U.S. Navy, or a northern corridor through Iranian waters.

Jakob Larsen, the chief safety and security officer at BIMCO, the world’s largest shipping association, said the memorandum of understanding signed on June 17 by the United States and Iran was problematic because it diminished the importance of international conventions regulating shipping, which allow for free passage of ships through international waterways. The agreement also did not address fundamental disagreements between the two countries, he said.

“At the same time, Iran retains the capability to target shipping with drones and missiles throughout the Strait and surrounding waters, and recent events suggest it is prepared to exercise that capability,” Mr. Larsen said.

Ship traffic through the strait, Mr. Larsen said, would likely remain low “for as long as the Iranian threat remains intact.”

“It is difficult to say how long it will take to reduce the Iranian threat to an acceptable level,” he added, “as it depends on several factors such as the U.S. capability and effort to physically destroy the threat, and the impact of renewed economic sanctions on Iran.”