UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 6-K

REPORT OF FOREIGN PRIVATE ISSUER

PURSUANT TO RULE 13a-16 OR 15d-16

UNDER THE SECURITIES EXCHANGE ACT OF 1934

For the month of June 2026

Commission File Number: 001-15092

TURKCELL İLETİŞİM HİZMETLERİ A.Ş.

(Translation of registrant’s name into English)

Turkcell Küçükyalı Plaza

Aydınevler Mahallesi, İsmet İnönü Caddesi, No:20

Küçükyalı B Blok Ofispark

34854 Maltepe
Istanbul, Türkiye

(Address of Principal Executive Offices)

Indicate by check mark whether the registrant files or will file annual reports under cover of Form 20-F or Form 40-F:

x Form 20-F  ¨ Form 40-F

Enclosure: A press release dated June 18, 2026 announcing the capital increase in the registrant's subsidiary, CJSC Belarusian Telecommunications Network.

Istanbul, June 18, 2026

Announcement Regarding the Capital Increase in BeST

The capital of our Company's subsidiary, CJSC Belarusian Telecommunications Network ("BeST"), has been increased by BYN 10,876,568.78 from BYN 1,363,865,668.50 to BYN 1,374,742,237.28. Our Company's pre-emption rights with respect to the capital increase have been fully paid.

For more information:

Turkcell Investor Relations

investor.relations@turkcell.com.tr

Tel: + 90 212 313 1888

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, Turkcell İletişim Hizmetleri A.Ş. has duly caused this report to be signed on its behalf by the undersigned, thereunto duly authorized.