This frame grab of footage aired Wednesday by Iranian state television shows a vessel that ran aground in the Strait of Hormuz. (Iranian state television via AP)

DUBAI, United Arab Emirates (AP) — Iran’s joint military command warned Thursday that all oil tankers moving through the Strait of Hormuz must use its approved routes or face a “forceful response,” ratcheting up tensions again over a waterway crucial for international energy supplies.

The strait, the narrow mouth of the Persian Gulf, has emerged as one of the top issues in negotiations seeking a permanent end to the Iran war. The statement from the Khatam al-Anbiya military command, reported by Iranian state television, comes after both U.S. and Iranian diplomats met with mediators Wednesday in Qatar.

Iran is preparing for the funeral of the late Supreme Leader Ayatollah Ali Khamenei, who was killed in the war’s first moments in February. On Thursday night, Iranian state media broadcast images of what it said was the casket with Khamenei’s remains arriving at the Imam Khomeini Hussainiya, for the farewell ceremony.

Hundreds were seen in the footage, praying and grieving near the casket covered with a green cloth. The weeklong official funeral is expected to start on Saturday.

It wasn’t clear what sparked Iran’s warning Thursday about oil tankers moving through the Strait of Hormuz. However, the U.S. military’s Central Command had put out a statement about a meeting with officials from Mideast nations in Bahrain that said “leaders underscored their shared commitment to the free flow of commerce through” the strait.

That could have been the phrase that angered Iran.

“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 Iranian statement said.

It also said that interference by U.S. forces in the strait “will be met with a rapid and decisive reaction.”

Iran and the United States agreed as part of an interim deal to allow ships to pass without paying charges for 60 days. But Tehran insisted it must control the routes of the vessels and later charge fees for passage, upending decades of practice in the waterway.

The U.S. and many Gulf Arab states say they won’t agree to Iran charging for passage through the strait. An effort by Oman and a United Nations agency to launch a new route near Oman’s shore sparked attacks across the Mideast last weekend, highlighting the tensions.

Despite the attacks, ship traffic in the strait continued to rebound. At least 258 ships transited the waterway last week, a period that included Iranian strikes on two commercial vessels, according to marine data and analysis company Lloyd’s List Intelligence. That’s up from 138 ships the previous week.