Oman says it is working to contain an oil spill off its southern coast after a tanker ran aground in June inside a protected marine area, triggering calls for action by environmentalists, according to AFP.

It follows an investigation by AFP that found the ship had been stranded for weeks near al-Qibliyyah island after it was rocked by explosions. The Oman Environment Authority says the ongoing spill has affected roughly 390 square kilometres, according to its most recent analysis.

A report in the state-backed Oman News Agency quoted an official with the transport ministry as saying authorities were conducting aerial surveillance and had deployed divers. The official said authorities were in the early stages of developing a plan to transfer the vessel’s oil cargo.

Omani authorities have not yet identified the cause of the spill. But British maritime security company Vanguard told AFP last week that the tanker was rocked by explosions in early June as it sailed off the coast of Yemen, causing water to enter several sections of the vessel.