Shell workers at Nigeria’s Bonga oil field in the southern Niger Delta were evacuated following a militant threat, a labor union official said as the vice president met oil majors to discuss a surge in violence, Reuters reported.

Days before, a nee group of militants called the Niger Delta Avengers, attacked a Chevron facility in the impoverished Delta, where tensions have been building up since authorities issued an arrest warrant in January for a former militant leader on corruption charges.

The Nigerian newspaper Vanguard reported that a skeleton crew was left behind, though operations at the Shell facility were suspended. The staff and facility are protected by two gunboats belonging to the Military Joint Taskforce.

Meanwhile, Nigeria’s Vice President Yemi Osinbajo met executives from Shell, France’s Total, and Italy’s Agip and Chevron. However all declined to talk to the press. “All of us as stakeholders are concerned and we have agreed to work together to ensure that production is not disrupted,” said Henry Dickson, governor of the oil-producing Bayelsa state in the Delta, who took part in the meeting. “This is a time that we cannot afford to have any disruption, not to talk of vandalism of critical national assets,” he added.