Production of Nigeria’s benchmark Qua Iboe BFO-QUA crude oil grade has been reduced due to a pipeline problem, two traders said on Thursday.

Operator Exxon did not immediately respond to a request for comment.

Qua Iboe is Nigeria’s largest grade of crude oil and was set to account for 317,000 barrels per day of exports in June.

It was not immediately clear by how much the pipeline problem had reduced output.

The reported reduction of Qua Iboe came as Nigeria’s production slumped to a 22-year low the previous session as Shell declared a force majeure on the Bonny Light grade of crude oil due to sabotage on a pipeline.

Last week, a group known as Niger Delta Avengers attacked a Chevron facility in the Delta after also claiming a strike in February against a Shell pipeline, which shut down the 250,000 bpd Forcados export terminal.

A trader said he had been told the problem with the Qua Iboe was caused by unintentional damage rather than sabotage.