Lawyers for eight communities from Nigeria's oil-producing Niger Delta have filed suit demanding that international oil firms stop burning off gas - a process known as "flaring."

Activists argue that flaring pollutes the environment and contributes to global warming. The Nigerian government and oil companies have promised to phase out the practice over the next several years.

But oil giant Royal Dutch Shell has admitted its plan to stop burning off gas from its wells and rigs - which produces huge orange flames following by dense black smoke - is behind schedule.

Nigeria is Africa's biggest oil producing nation, pumping an estimated 2.3 billion barrels of crude per day.

Some information for this report provided by AFP.