Japan's transport safety authority concluded Thursday a cargo ship ran aground and spilled oil off Mauritius in 2020 because it altered its planned route and approached the coast in order to pick up mobile phone signals.

The Japan Transport Safety Board also said that COVID-19 travel restrictions and border closures may have slowed containment efforts and increased the damage caused by the massive oil spill.

The bulk carrier Wakashio, chartered by Mitsui O.S.K. Lines and owned by Nagashiki Shipping in Okayama Prefecture, spilled about 1,000 tons of fuel oil into a pristine marine environment in the Indian Ocean.