Just days after the U.S. and Iran signed a memorandum of understanding to reopen the Strait of Hormuz, Tehran announced the critical waterway is closed again, threatening oil flows after they had barely started to rebound.

On Saturday, Iran’s military command said it closed the strait, citing continued Israeli attacks on Lebanon and U.S. “bad faith” in failing to uphold commitments to end the war. It also warned that “if the aggression continues, subsequent steps have been planned.”

Not to be outdone, President Donald Trump threatened to charge U.S. tolls for “services rendered as the Guardian Angel to the countries of the Middle East,” if a final deal with Iran isn’t reached in 60 days.

That came after the start of talks between the two countries had been delayed while both sides also sought to assert influence over the strait.

U.S. Central Command insisted safe passage through the strait remained intact and that traffic is up, with 55 merchant ships loaded with cargo and 17 million barrels of oil transiting on Saturday.

It added that U.S. forces are still operating in the area to support freedom of navigation and pointed out that the Joint Maritime Information Center issued an advisory on Thursday affirming that a southern route along Oman’s coast is safe.

While the U.S. ended its naval blockade on Iran as part of the MOU, Central Command also said “U.S. forces remain present and vigilant to ensure all aspects of the agreement with Iran are adhered to, obeyed, and in full force and effect.”

For its part, Tehran’s new Persian Gulf Strait Authority warned that ships must follow a regime-established route that passes along the Iranian coast and that alternatives are prohibited.

And despite its deal with the U.S. banning tolls for 60 days, the PGSA is requiring insurance that will eventually come at a cost.

“At present, this insurance is provided free of charge to the vessel owner, with all expenses covered by the Islamic Republic of Iran,” Iran said. “The PGSA reserves the right to introduce insurance fees in the future, which will be determined by the relevant insurer. Owners will then be required to purchase and renew coverage accordingly.”

For ships that require assurances of safe passage, recent developments aren’t helping. Oil prices tumbled after the U.S. and Iran announced the deal last weekend, but a return to normal flows will take months.

And until supplies recover, global oil inventories will continue to remain under pressure. In the U.S., the Strategic Petroleum Reserve has already plunged to the lowest level since 1983.

The situation in the Strait of Hormuz, which was the scene of regular skirmishes between the U.S. and Iran before the latest deal, highlights the private sector’s role.

“But it’s not Iran or the US who decide that the strait is open—it’s shipping and insurance companies,” Eurasia Group senior analyst Gregory Brew posted on X.

While other Iran experts predicted Saturday’s announcement of the strait’s closure would scare off ships just as traffic was showing signs of climbing, Brew questioned if that will be a sufficient threat.

Again, it’s up to the ships to decide.

“Will the Iranian announcement be enough to deter them? Or will Iran need to resort to force and directly violate the MOU’s terms?” he added.

Even before the latest flurry of mixed signals, the industry had doubts. One shipping executive told the New York Times on Friday that he deemed the conditions too uncertain for his ship to leave the Persian Gulf.

Underwater mines also remain a threat, along with navigational risks like collision, especially if there’s a mass rush among ships to try exiting at once.

German shipping company Hapag-Lloyd told the Times that its vessels still in the Persian Gulf were ready to go but still waiting.

“No indication right now when we would move,” a spokesman said on Friday.

To be sure, the Strait of Hormuz is Iran’s main source of leverage, and the regime’s announcement that it’s closed again could be timed for the start of negotiations with the U.S., according to Brew.

Indeed, Iran demonstrated it can shut down the strait despite heavy U.S. and Israeli bombardment during the war. At the same time, the U.S. has also tried to tout its ability to defend the alternate route near Oman.

Earlier this month, Trump described a “secret mission” that he claimed had put more than 100 million barrels of oil on the market, or about five day’s worth of shipments before the war started.

“I can say it now. Something you didn’t know,” he said. “Do you know we’ve been taking out millions of barrels of oil? Nobody knows it. You know who doesn’t know about it? Iran — until right now.”

This story was originally featured on Fortune.com