Nigeria, Jan. 26 -- The bribery trial of former Nigerian petroleum minister Diezani Alison-Madueke-that U.K. investigators describe as a major step in a long-running international corruption probe-started Monday at Southwark Crown Court in London, with the first substantive hearing expected Tuesday.

Alison-Madueke, who served as Nigeria's oil minister from 2010 to 2015 and later chaired the Organization of the Petroleum Exporting Countries (OPEC) in 2014-2015, faces six charges, including five counts of accepting bribes and one count of conspiracy to commit bribery. All charges are linked to the awarding of oil and gas contracts during her time in office, according to U.K. authorities and media reports.

British investigators allege she ...