Iran’s joint military command issued a stern warning on Thursday that all oil tankers traversing the Strait of Hormuz must adhere to its designated routes or risk a “forceful response,” escalating tensions once again over a strategic waterway that is vital to global energy supplies.

The narrow mouth of the Persian Gulf has become a central flashpoint in ongoing negotiations aimed at securing a permanent end to the conflict with Iran. The statement from the Khatam al-Anbiya military command, which was carried by Iranian state television, followed meetings between U.S. and Iranian diplomats with mediators in Qatar on Wednesday. The exact trigger for the latest threat remains unclear, though it may have been prompted by a U.S. Central Command statement following a meeting with Middle Eastern officials in Bahrain, in which “leaders underscored their shared commitment to the free flow of commerce through” the strait. The timing also coincides with Iran’s preparations for the funeral of the late Supreme Leader Ayatollah Ali Khamenei, who was killed in the early stages of the war in February.

The Iranian military’s warning left no room for ambiguity. “Any failure to comply, deviation from the designated route, or disregard for the navigation protocols of the Islamic Republic of Iran in the Strait of Hormuz will be met with an immediate and forceful response from the armed forces, endangering the security of the violating vessels,” the statement read. It further cautioned that interference by U.S. forces in the strait “will be met with a rapid and decisive reaction”.

Under an interim agreement, Iran and the United States had allowed ships to transit without paying charges for 60 days. However, Tehran has since insisted on controlling vessel routes and eventually imposing passage fees, upending decades of established practice in the waterway. The U.S. and many Gulf Arab states have rejected Iran’s demand to charge for passage through the strait. An effort by Oman and a United Nations agency to establish a new route near Oman’s shore over the weekend only heightened tensions, sparking attacks across the Middle East.

Despite the attacks, shipping traffic in the strait has shown signs of recovery. At least 258 ships transited the waterway last week, a period that included Iranian strikes on two commercial vessels, according to marine data firm Lloyd’s List Intelligence. That marks an increase from 138 ships the previous week. Iran’s attacks on June 25 and 27 “seem to have been forgotten,” Richard Meade, editor-in-chief at Lloyd’s, said during a webinar on Thursday. However, traffic remains far below pre-war levels, when about 130 vessels passed through daily. With ship operators forced to choose between complying with Iran’s demands or risking the route off Oman under U.S. watch, “nothing about this situation is stable,” Meade warned. “Routes are being chosen on an hour-by-hour basis … and they are contingent on shifting political approvals and real-time security assessments,” he added. “This is not the new normal”.

Earlier this week, Iranian state television reported that a foreign ship became stuck in the strait after ignoring instructions from Iran’s paramilitary Revolutionary Guard. However, the vessel’s shape and reported location suggest it is connected to Iran and appears to have been stranded for months.

Despite the heightened tensions, Wednesday’s diplomatic talks in Qatar saw “positive progress,” according to Pakistani Foreign Ministry spokesperson Tahir Andrabi. He told journalists that Pakistan hopes the next round of talks will be scheduled as soon as possible after Khamenei’s funeral.