Supporters of the main opposition Republican People's Party (CHP) gather in front of the party's headquarters to celebrate the municipal elections results in Ankara, Turkey, March 31, 2019. REUTERS/Stringer

ANKARA (Reuters) - Turkish President Tayyip Erdogan’s AK Party (AKP) and the main opposition Republican People’s Party (CHP) on Monday both declared they had narrowly won Istanbul’s mayoral elections on Sunday.

Speaking to reporters in Istanbul, CHP candidate Ekrem Imamoglu, citing his party’s data, said he had won by nearly 28,000 votes. Minutes later, the AKP provincial head in Istanbul said his party’s candidate, Binali Yildirim, had won by around 4,000 votes.