The value of the three-year deal was not disclosed.
Avangard will be the sole supplier of missiles for the S-400 system, the ministry said. The types of missiles in question were not disclosed but previous descriptions of S-400 have included the designations 9M96 and 9M96E2 and the long-range 40N6E.
The Russian military has previously said the S-400 system would not be exported.
The S-400 Triumph, which succeeds the Soviet-era S-300, is a medium- to long-range surface-to-air missile system that can effectively engage any aerial target, including aircraft, unmanned aerial vehicles, and cruise and ballistic missiles at up to 400 kilometers and an altitude of up to 30 kilometers.