Nigeria minister wants Delta grievances addressed as Chevron attacked.

LAGOS/YENAGOA, Nigeria (Reuters) - Nigeria's government needs to address grievances in the oil-producing Niger Delta, its oil minister said on Thursday, hours after a Chevron source said a militant attack had forced it to shut its onshore operations in the restive region.

A militant group called the Niger Delta Avengers, which has told oil firms to leave the Delta before the end of May, said late on Wednesday that it had blown up the Chevron's facility's mains electricity feed. Its attacks have hobbled oil output over the past month.

A company source told Reuters that "all activities in Chevron are grounded" onshore while oil industry sources said roughly 90,000 barrels per day (bpd) of Escravos were gone due to the latest attack and another on Chevron's offshore facilities earlier this month. Planned Escravos exports in the first half of 2016 averaged 167,000 bpd.

A Twitter account with the group's name said late on Wednesday: "We Warned #Chevron