Rosaviakosmos just announced that the next launch of a military satellite is scheduled for 13:59 MSK on September 2nd. The launcher, Soyuz-U, will be moved to the launch pad No. 6 of the launch complex No. 31 at Baykonur after August 31st.
It looks like the Soyuz-U will launch a Yantar-1KFT/Kometa optical reconnaissance satellite.