Militants launched new attacks in the Niger Delta on Thursday, June 2 vowing to bring Nigeria's struggling oil industry to a halt, and the president cancelled a long-awaited visit to the region, Reuters reports.

The army said militants killed six people on Wednesday, June 1 when they ambushed a boat belonging to state oil firm NNPC in the Warri area.

Separately, the Niger Delta Avengers group said it had attacked two crude pipelines operated by Italy's ENI.

"At about 2:00 am today @NDAvengers blew up the Ogboinbiri to Tebidaba and Clough Creek to Tebidaba Crude Oil pipelines in Bayelsa State," the group said on Twitter.

"This is in line with our promise to all international oil companies and indigenous oil companies that Nigeria oil production will be zero."

The group also said on Friday it has again blown up the Forcados oil pipeline, which was under repair after an attack in February, Reuters says.

"At 3:00 am today @NDAvengers blew up the SPDC Forcados 48" Exportline," the group said on a Twitter feed it uses to claim credit for attacks.

"We warned SPDC not to go ahead with repair works," the group said.

Nigerian President Muhammadu Buhari cancelled at the last minute a visit planned for Thursday to the Delta, source of most of Nigeria's crude, Reuters says.

Vice President Yemi Osinbajo made the trip in Buhari's place to launch a cleanup program in an area badly hit by oil spills, vowing to work with community leaders to end militant attacks.