TEHRAN (AFP) — Iran’s Revolutionary Guards on Thursday warned against any crossings of the Strait of Hormuz without authorization, saying vessels not complying “will be dealt with.”

The future of the strait, a vital route for energy shipments that was locked down by Iran during the war, is a key sticking point in negotiations between Tehran and Washington.

Tehran has said it plans to impose what it calls maritime service fees, as opposed to tolls, while the United States argues it is an international waterway and therefore should not be charged.

“The only authorized route for passage through the Strait of Hormuz is the route announced by the Islamic Republic of Iran,” said the Revolutionary Guards, the ideological arm of Iran’s military.

Any crossing without authorization is “unacceptable and extremely dangerous,” they warned in a statement.

They also denounced what they said was a new route through the waterway announced by “certain authorities,” without elaborating.

Hormuz is a narrow stretch of water between Iran and the Gulf countries through which roughly 20 percent of the world’s crude oil and liquified natural gas normally transits.

At its narrowest it is only about 30 kilometers wide.

The only route currently authorized by Iran runs through a corridor that follows the country’s coast.

A memorandum of understanding signed last week by Tehran and Washington to end their war stipulates that commercial ships may transit the strait free of charge for the next 60 days.

With Iran and the US in negotiations, it is unclear what arrangements will be in place after that period.

Iran and Oman, which also borders the strait, announced on Tuesday that they would study the “costs” to be charged for services related to administration of the strait.

But US Secretary of State Marco Rubio, visiting neighboring Gulf countries this week, said Washington would not accept any tolls or fees.

Evacuation route

Traffic through the Strait of Hormuz continued to improve compared to pre-US and Iran agreement levels on Tuesday, with some ships crossing through a new IMO evacuation route, tracking data showed.

As of 1500 GMT on Wednesday, maritime tracking firm Kpler recorded 25 transits by commodity ships on Tuesday, and 17 so far on Wednesday.

Total figures are likely to rise further, as crossings are identified retrospectively, notably through satellite imagery.

Tuesday’s crossings fall short of the 38 commodities transits detected on Monday, the highest amount since the Strait of Hormuz was closed down by Iran on 1 March at the start of the Middle East war.

However, Tuesday’s crossings continue to suggest an improvement in traffic compared with figures before the US and Iran agreed to a memorandum of understanding on 14 June.

Since 15 June, on average 22 ships have crossed every day according to Kpler, compared with less than 10 daily transits between 1 March and 14 June.

In peacetime, around 120 ships normally pass through the Strait of Hormuz each day, carrying about a fifth of global oil and LNG gas exports, making it one of the world’s most important waterways.