Royal Dutch Shell has resumed operations at its Utorogu gas plant in Nigeria three days after it was shut down to repair a pipeline that was tapped by thieves, a spokesman said on Monday.

The facility's brief closure caused the OPEC member's already intermittent power generation to fall by more than 20 percent. It began resending gas supplies to several power stations in Africa's most populous country on Saturday.

We've repaired the pipeline. The plant resumed gas supplies on Saturday, Shell spokesman Precious Okolobo said.

The cut in supplies from the plant, in the southern state of Delta, forced the Power Holding Company of Nigeria to shut down three power stations and reduce operations in a fourth.

The state-run electric company said power generation fell by more than 700 megawatts to around 2,500 MW.

Despite being Africa's largest oil producer, Nigeria's power system is in shambles due to decades of corruption and mismanagement. Much of Nigeria goes without electricity for weeks at a time, leaving residents to rely on expensive gasoline-powered generators.

The power problems in Nigeria, home to 140 million people, are one of the main brakes on economic growth in sub-Saharan Africa's second-biggest economy. (For full Reuters Africa coverage and to have your say on the top issues, visit: ) (Reporting by Randy Fabi; Editing by Nick Tattersall)