Nigeria's grid operator has resorted to selective load shedding to prevent a nationwide blackout after electricity output fell due to a strike by oil and gas workers that disrupted fuel supplies to power plants, it said on Tuesday.

The Petroleum and Natural Gas Senior Staff Association of Nigeria (PENGASSAN) is striking to protest the sacking of more than 800 unionised staff at the Dangote refinery.

That has triggered widespread gas shortages, which the Nigerian Independent System Operator (NISO) said had led generation on the national grid to fall to a low of about 3,200 MW from more than 4,300 MW early on Sunday.

(Reporting by Camillus Eboh; Writing by Elisha Bala-Gbogbo; Editing by Jan Harvey)