Boko Haram Islamic extremists fired repeatedly at a military helicopter on a humanitarian mission in northeast Nigeria and wounded one airman, the Nigerian Air Force said Thursday.

A fighter jet and helicopter gunship were immediately scrambled and retaliated, killing scores of the insurgents at the located threat, spokesman Group Capt. Ayodele Famuyiwa said in a statement.

He said the Mi-17 transport helicopter was carrying medical personnel from Maiduguri city to treat refugees in the Gwoza area when it came under repeated fire on Wednesday.

But the pilot was able to continue the flight safely and the attack didn't interrupt a two-day medical outreach program.

Boko Haram in 2014 shot down a Nigerian Air Force fighter jet and beheaded its pilot. The extremists are armed with anti-aircraft guns stolen from Nigeria's military.

A multinational force of troops from Nigeria and its neighbors last year drove Boko Haram out of occupied towns and villages in northeast Nigeria but isolated attacks and suicide bombings continue.

The seven-year Islamic uprising has killed more than 20,000 people and driven 2.6 million from the homes, creating the worst humanitarian crisis on the continent with millions facing starvation.

AP