Turkey's electoral board has rejected a demand by opposition parties to annul local election results in Istanbul's 39 districts, following the board's decision to strip the opposition of its victory in the mayoral race.

The Supreme Electoral Board on Monday also turned down the opposition's request to annul the results of last year's presidential and parliamentary elections, which further solidified President Recep Tayyip Erdogan's grip on power.

The board ruled in favor of Erdogan's party last week, ordering a re-run of the mayoral race on June 23, saying some officials overseeing the election weren't civil servants as required by law.

The opposition had argued that the board's decision on ballot box committees should apply to all results in Istanbul, where Erdogan's party won a majority of districts.