The French telecommunications company Iliad has made a surprise offer for T-Mobile, setting up a potential bidding war with Sprint, the U.S. mobile carrier now controlled by SoftBank.

The approach will further shake up a U.S. media and telecommunications market already in tumult as a series of U.S. cable and cellular operators bid for rivals to cut costs amid slowing growth. The market and its relatively healthy margins remain alluring to some foreign operators like SoftBank and Iliad, however.

Iliad, which has shaken up the French mobile and broadband market in the past decade with its cheap no-frills subscriber plans, bid $15 billion in cash for 56.6 percent of T-Mobile at $33 per share, it said in a statement Thursday.