An unspecified number of workers at a Nigerian cement factory owned by Africa’s richest man have been abducted, police said, after a staff bus they were commuting in was attacked by armed men.

Three Aliko Dangote employees were shot during Monday’s attack in the Okpella area of Edo state in southern Nigeria and are in the hospital, said state police command spokesman Chidi Nwabuzor in a statement on Tuesday.

“The hoodlums suspected to be kidnappers took some of the passengers into the bush,” Nwabuzor said, without providing the exact number of staff that were seized. “The divisional police officer mobilized his operatives, vigilantes group and the hunters into the forest for a vigorous bush-combing operation to rescue the victims.”

Dangote Industries has not commented on the incident and a spokesman did not immediately respond to requests for comment.

The abduction of the Dangote staff adds to recent incidents targeting workers in the oil producing state in Nigeria’s Niger Delta region, where more than 90% of the nation’s oil resources are extracted.

Gunmen killed three staff of Okomu Oil Palm Co. Plc on May 6 in the same state, the company said. Four other workers were wounded in another attack on May 7, which the company said was repelled by its security personnel.

President Bola Tinubu campaigned on a promise to end insecurity in the country, but it continues to be a problem as he nears the anniversary of his first year in office.