OSLO - More than a dozen tankers, including three sanctioned vessels, passed through the Strait of Hormuz after a 50-day blockade was lifted on Friday, shipping data showed, before Iran reimposed restrictions on Saturday and fired at some vessels.

Reopening the strait is key for Gulf producers to resume full oil and gas supplies to the world, and end what the International Energy Agency has called the worst-ever supply disruption.

U.S. President Donald Trump said on Friday Iran had agreed to open the strait, while Iranian officials said they wanted the U.S. to fully lift its blockade of Iranian tankers.

Western shipping companies cautiously welcomed the announcements but said more clarity was needed, including on the presence of sea mines, before their vessels could transit.

IRAN RESUMES RESTRICTIONS

The ships that passed through the strait on Friday and Saturday via Iranian waters south of Larak island were mainly older, non-Western-owned vessels and included four sanctioned ships, according to ship-tracking data.

Iran arranged passage for a limited number of oil tankers and commercial ships following prior agreements in negotiations, a spokesperson for Iran's Revolutionary Guards said.

Other ships have been seen approaching the strait and turning back as Iran said it would maintain strict controls as long as the U.S. continues its blockade of Iranian ports.

The UK Navy reported on Saturday that Iranian gunboats fired at some ships attempting to cross the strait.

Some merchant vessels received radio messages from Iran's navy saying the strait was shut again and that no ships were allowed to pass, shipping sources said on Saturday.

Ship-tracking data showed five vessels loaded with liquefied natural gas from Ras Laffan in Qatar approaching the strait on Saturday morning.

No LNG cargoes have transited the waterway since the U.S.-Israeli war with Iran began on February 28.

Hundreds of ships have been stuck in the Gulf since the conflict started and Tehran closed the strait, forcing Gulf oil and gas producers to sharply cut production.

Top producers such as Saudi Arabia, the UAE, Iraq and Kuwait say they need steady tanker flows and unrestricted passage through the strait to resume normal export operations.

-Reuters bureaus. writing by Dmitry Zhdanikov. Editing by William Mallard, Emelia Sithole-Matarise and Mark Potter/Reuters