Turkey's state-run news agency says prosecutors have launched investigations into alleged irregularities during local elections in Istanbul that resulted in a narrow victory for the opposition.

Anadolu Agency said Thursday authorities want to question more than 100 people for alleged fraud during the vote count and the entering of data in three Istanbul districts.

The move comes as President Recep Tayyip Erdogan's ruling party presses ahead with efforts to have the March 31 Istanbul election results annulled over the alleged irregularities and for the vote there to be repeated.

In a major blow to Erdogan, the ruling party lost its decades-long hold over Istanbul and the capital Ankara to the opposition.

Turkey's top electoral body was expected to consider on Monday a possible re-run of the vote.