Announcing the deal, Sistema, which already owns 53% of MTS, said it bought the additional shares between September 5 and October 15 2013.
The transactions amounted to 6.425 million shares, or 0.3% of MTS ordinary shares on the open market between, according to the firm.
MTS claims to be the leading telecoms group in Russia, Eastern Europe and Central Asia, offering mobile, fixed-line, broadband, pay TV, content and entertainment services.
Sistema invests in and is a major shareholder of companies serving more than 100 million customers in the sectors of telecoms, technology, oil and energy, radars and aerospace, banking, retail, mass-media, tourism and healthcare services.
Founded in 1993, the company reported revenues of US$8.5 billion for the second quarter of 2013, and had total assets of US$44.4 billion as of June 30, 2013.