6-K

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 6-K

REPORT OF FOREIGN PRIVATEISSUER

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

SECURITIES EXCHANGE ACTOF 1934

For the month of January, 2023.

Commission File Number: 001-38763

MILLICOM INTERNATIONAL CELLULAR S.A.

(Exact Name ofRegistrant as Specified in Its Charter)

2, Rue du Fort Bourbon,

L-1249 Luxembourg

Grand Duchy of Luxembourg

(Address of principalexecutive office)

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

Form 20-F  ☒       Form 40-F  ☐

Indicate by check mark if the registrant is submitting the Form 6-K in paper as permitted by Regulation S-T Rule 101(b)(1):

Yes  ☐       No ☒

Indicate by check mark if the registrant is submitting the Form 6-K in paper as permitted by Regulation S-T Rule 101(b)(7):

Yes  ☐       No ☒

MILLICOM INTERNATIONAL CELLULAR S.A.

INDEX TO FURNISHED MATERIAL

Item

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Millicom confirms discussions on a potentialtransaction

LUXEMBOURG, January25, 2023 – As a response to market speculation, the Board of Directors of Millicom International Cellular S.A. confirms that a potential acquisition of all outstanding shares in Millicom is being discussed with Apollo Global Management and Claure Group.

There is no certainty that a transaction will materialize nor as to the terms, timing or form of any potential transaction.

-END-

For further information,please contact:

About Millicom

Millicom (NASDAQ U.S.: TIGO, Nasdaq Stockholm: TIGO_SDB) is a leading provider of fixed and mobile telecommunications services in Latin America. Through our TIGO® and Tigo Business® brands, we provide a wide range of digital services and products, including TIGO Money for mobile financial services, TIGO Sports for local entertainment, TIGO ONEtv for pay TV, high-speed data, voice, and business-to-business solutions such as cloud and security. As of December 31, 2022, Millicom employed approximately 20,000 people and provided mobile and fiber-cable services through its digital highways to more than 45 million customers, with a fiber-cable footprint over 13 million homes passed. Founded in 1990, Millicom International Cellular S.A. is headquartered in Luxembourg.

Regulatory Statement

This information was prior to this release inside information and is information that Millicom is obliged to make public pursuant to the EU Market Abuse Regulation. This information was submitted for publication, through the agency of the contact person set out above, at 17:00 CET on January 25, 2023.

SIGNATURES

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

Date: January 25, 2023