Tankers face a higher risk of attack in the Strait of Hormuz after Iran warned it would block routes it has not authorised, sources told Reuters.

A senior regional official close to Tehran told the agency that Iran has warned regional countries that any attempt to open new routes for oil exports would be treated as hostile. Last week saw the largest number of attacks on tankers in the waterway since the Iran war began, and the number of vessels attempting the passage fell to its lowest in more than two months, Reuters reported.

The British naval agency UKMTO said projectiles struck a tanker about 51 nautical miles off the coast of Qatar. Maritime security sources said the Antigua and Barbuda-flagged chemical tanker Acers was hit and that crew members sustained minor injuries.

Jakob Larsen, chief safety and security officer at the shipping association BIMCO, said the recent attacks seemed to have reduced shipowners’ appetite to sail through the strait.

The strait is a key route for the world’s oil, so disruption there can push up fuel prices, which affects import costs for Sri Lanka. Danish shipping group Maersk said on Thursday it was raising its emergency fuel surcharge on inland transport in the UK and Ireland because of the conflict in the Middle East.

Industry executives told a forum in London this week that accessible oil stocks are running low.