Hundreds of vessels were seen clustering near Dubai on May 5, as more ships moved away from a still-empty Strait of Hormuz in response to Iran’s efforts to widen its area of control.

A weeks-long ceasefire between the U.S. and Iran has begun to look increasingly fragile, with the two sides exchanging fire as Washington said it had opened a passage through the waterway, and CBS reported two American destroyers had crossed into the Persian Gulf.  

Since May 4, nearly 60 vessels across different types sailed into an area off Dubai monitored by Bloomberg News — an unusually large number even for waters that have seen carriers clustering since the start of the war. At least 363 ships are currently in the area, according to their signals, compared with an average of 294 the seven days prior. 

Dubai falls just outside the new Hormuz control area defined by Tehran, which extends south from the strait to Umm al-Quwain, along the United Arab Emirates coast and inside the gulf.

The Strait of Hormuz was nearly empty on May 5, as ships clustered around Dubai.

Monitoring vessels in the Persian Gulf has been complicated since the start of the war by the number of ships going “dark,” or switching off transponders, and by increased electronic interference, as evidenced by the emergence of oddly-shaped clusters of ships. The exact shape of the cluster around Dubai, therefore, may not capture reality on the water perfectly, but will show the trend in maritime movement.

The grouping has increased over the last day, as crew members report radio broadcasts warning vessels of new boundaries defended by the Islamic Revolutionary Guard Corps. Attacks on the United Arab Emirates port of Fujairah in the Gulf of Oman, meanwhile, have underscored the expanded Iranian command zone — and kept the strait largely devoid of traffic through the morning of May 5.

“The U.S. is attempting to level the power balance in the strait and that’s been reciprocated against by Iran. It’s escalation,” said Anoop Singh, global head of shipping research at Oil Brokerage Ltd. “I’m not expecting a quick reopening of bi-directional flows through the strait.”

Hormuz, a vital energy thoroughfare, has become a flashpoint in the nine-week war. Traffic has dwindled since the start of U.S. and Israeli strikes on Iran, but it oscillates each time one side has tried to adjust levels of control.

The number of daily Hormuz passages is currently at near zero — compared with around 135 each day before the war.

The extended lockdown of Hormuz has already upended global freight markets, with decades-old benchmarks turning irrelevant overnight. If the U.S. succeeds in guiding more ships out of the strait, the prospect of an exit for the hundreds of oil and chemical carriers trapped in the gulf could alleviate pressure on the market, said Singh.

Events so far this week, however, have only encouraged caution from the shipping industry. The UAE’s state oil company, Abu Dhabi National Oil Co., confirmed on May 4 that its supertanker, Barakah, was hit by drones while in Hormuz, and South Korea said that one of its ships was targeted for the first time during the war.