TKC 6-K

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 November 2025

Commission File Number: 001-15092

TURKCELL İLETİŞİM HİZMETLERİA.Ş.

(Translation of registrant’s name into English)

Turkcell Küçükyalı Plaza

Aydınevler Mahallesi İnönü Caddesi No:20

Küçükyalı 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 November 6, 2025 announcing the decision of the registrant’s board of directors to issue debt instruments.

Istanbul, November 6, 2025

Announcement Regarding the Board of DirectorsDecision to Issue Debt Instruments

Our Company's Board of Directors resolved to issue debt instruments up to a nominal amount of TRY 15 billion, in Turkish Lira terms, in the domestic markets, with various maturities of up to 2 years (inclusive), in one or more tranches, at a discount and/or fixed or variable coupon rates depending on market conditions, without a public offering, as private placement, and/or to be sold to institutional investors, pursuant to articles 3/2(3) and 25 of the Articles of Association of our Company and in line with the provisions of Communiqué on Debt Securities of Capital Markets Board. The respective issuance is subject to the approval of the Capital Markets Board.

For more information:

Turkcell Investor Relations

[email protected]

Tel: + 90 212 313 1888

Disclaimer

This press release does not constitute an offerto sell, or a solicitation of offers to purchase or subscribe for securities in the United States or any other jurisdiction in which suchoffer or solicitation would be unlawful. The securities referred to herein have not been and will not be registered under the U.S. SecuritiesAct of 1933, as amended (the "Securities Act"), and may not be offered, sold or delivered within the United States or to orfor the benefit of, U.S. persons (as defined in Regulation S under the Securities Act) absent registration or an applicable exemptionfrom the registration requirements of the Securities Act. This press release is being issued pursuant to and in accordance with Rule 135cunder the Securities Act.

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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.