Nigeria has arrested seven people for allegedly providing the Niger Delta Avengers (NDA) militants with high-caliber explosives and detonators.

The militant group has been conducting sabotage activities against Nigeria’s oil facilities since March.

On Thursday, Nigeria’s National Security Adviser Major-General Mohammed Monguno said the staff of an explosives-distribution company in the Niger Delta had diverted the explosives to the militants.

"A detailed audit of the records of explosives magazines and quarries in that region was conducted, which revealed the diversion of about 9,000 kg of high explosives and 16,420 pieces of detonators for illegal use," he said.

"The actors, including the storeman of a major explosives distribution company in Nigeria, an accomplice and five security operatives, have been arrested and handed over to the appropriate authorities."

The Nigerian security official also stated that an investigation has been launched into the matter, adding, "I can assure you that they are deeply culpable and necessary action will be taken on the conclusion of these investigations."

"Any individual or company that operates outside the confines of legitimacy or legality will have itself to blame, and we want to add that the government of the day will not listen to... any company that decides to sabotage national security."

The militant group, mainly operating in the Niger Delta, publicly announced existence in March and since then has been blowing up gas and crude oil pipelines belonging to the Nigerian National Petroleum Corporation (NNPC).

The NDA attacks have had an immediate and significant impact on Nigeria’s wealth, as they have pushed the country’s oil output to its lowest level in decades. Oil exports account for 70 percent of Nigeria's government revenue.

The militants want foreign oil companies out of the Niger Delta. They say they are fighting to protect the environment and to win locals a bigger share of the profits.