The Niger Delta Avengers - the fighters behind many of the 2016 attacks - said they had planned the assaults after giving up on talks to give their impoverished southern region a greater share of the oil revenue it produced.

“This round of attacks will be the most deadly and will be targeting the deep sea operations of the multinationals,” the group said in a statement in its website.

It said its targets, in the seas off the swampland delta region, would include the Bonga Platform and the Agbami, EA and Akpo fields. The militants also said they would target the Nigerian oil company Brittania-U.

Shell operates the Bonga and EA fields while Chevron is the operator of Agbami. Akpo stakeholders include Total, China’s CNOOC, Brazil’s Petrobras and Nigeria’s Sapetro.

Representatives of Shell and Chevron declined to comment and there was no immediate statement from the other companies.

Attacks on pipelines and other facilities in the Niger Delta in 2016 cut Nigeria’s crude production from a peak of 2.2 million barrels per day (mbpd) to near 1 mbpd - the lowest level seen in Africa’s top oil producer in at least 30 years.

That, combined with low oil prices, pushed the OPEC member into its first recession in a quarter of a century - crude sales make up two-thirds of government revenue and most of its foreign exchange.

The militants agreed to a ceasefire in August 2016 - a development that helped pull Nigeria back out of recession in the second quarter of last year. But they called off the truce in November.

Any resumption of attacks would pile pressure on Nigeria’s President Muhammadu Buhari who is also facing separatist groups in the southeast, Islamist militants in the northeast and elections in 2019. He has not said whether he will stand.

The government has held talks to address grievances over poverty and oil pollution in the Delta for more than a year but community groups say no progress has been made.

The militant group said talks “have not achieved any meaningful results”.

“While promising a brutal outpour of our wrath, which shall shake the coffers of the failed Nigerian nation, our demand unambiguously is for the government to restructure this country,” said the group, calling for the Niger Delta to have direct control over its resources.

Emmanuel Ibe Kachikwu, the minister of state for petroleum, declined to comment.

The Niger Delta Avengers bombed the Forcados sub-sea pipeline in 2016, a strike which involved the use of divers. No substantial attacks have been carried out by any groups in the Delta region since January 2017.