The militants have called for a greater share of Nigeria's oil wealth - which accounts for around 70 percent of national income - to be passed on to the region's communities, and for authorities to clean up areas blighted by oil spills.

The Niger Delta Avengers, a militant group which has carried out a series of attacks on Nigerian oil facilities in the last few months, on Sunday said it had mounted five attacks in the southern energy hub since Friday.

Attacks in the Niger Delta pushed crude production in the OPEC member to 30-year lows in recent weeks, although the Nigerian National Petroleum Corporation (NNPC) last week said output was rising due to repairs and because there had not been an attack since June 16.

In a series of messages on its Twitter feed, the group said on Friday night it attacked a pipeline connected to the Warri refinery operated by NNPC, adding that on Saturday night it blew up two lines close to Batan flow station in Delta state run by NPDC, a subsidiary of NNPC.

The Avengers also said two Chevron facilities close to Abiteye flow station, in Delta state, were attacked in the early hours of Sunday. NNPC and Chevron could not immediately be contacted to comment on the group's statements.

The militants have called for a greater share of Nigeria's oil wealth - which accounts for around 70 percent of national income - to be passed on to the region's communities, and for authorities to clean up areas blighted by oil spills.

In late June, petroleum ministry sources said a month-long truce had been agreed with militants but the Avengers, who have claimed responsibility for most attacks in recent months, later said they did not "remember" agreeing to a ceasefire.