Initially, the police suspected Indigenous People of Biafra or IPOB but the group denied its role in the attack, reported AFP.

On Wednesday,  the workers were being ferried in buses heading to a Shell gas plant in the area, Imo state police spokesman Michael Abatan told AFP news agency.

“We lost one policeman and six oil workers in the attack by the gunmen,” he said.

Police have launched a probe to arrest the attackers and ascertain their motive.

The attack came on the same day President Muhammadu Buhari signed into law a new energy bill that aims to provide oil companies with a clearer framework for investing and working in Nigeria, the report stated.

“We have since shut down the project site while the incident has been reported to the police for investigation,” said SPDC, the Nigerian subsidiary of Shell, while confirming the attack.

Currently, Nigeria is faced with several security challenges, including a 12-year-long armed rebellion in the northeast, kidnappings for ransom and banditry in the northwest, herder-farmer violence in northern and central states, and separatist agitations in the southeast, according to the report.