A tanker reported being attacked by two Iranian gunboats 20km northeast of Oman today, a UK maritime agency said, while the master of a container ship reported sighting a splash in close proximity of the vessel about 3km east of Oman.

At least two merchant vessels said they were hit by gunfire as they attempted to cross the strait, Reuters reported, quoting three maritime and shipping sources.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.

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.

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.

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, Reuters reported quoting 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 were seen approaching the strait and turning back earlier today, as Iran said it would maintain strict controls as long as the U.S. continues its blockade of Iranian ports.

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.