moscow u.s. undersecretary state thomas shannon travel helsinki sept. 10-12 meet russian deputy foreign minister sergei ryabkov u.s. department state say saturday meet address areas bilateral concern cooperation say statement shannon also lead u.s. interagency delegation u.s.-russia strategic stability talk add quote unnamed russian diplomat russian news agencies report early saturday ryabkov-shannon meet helsinki would take place sept. 11-12. relations moscow washington low point since cold war strain russia annexation crimea 2014 subsequent separatist conflict eastern ukraine developments lead washington impose economic sanction russia u.s. president donald trump battle allegations associate collude russia grudgingly sign law new sanction moscow draw congress u.s. undersecretary shannon russian deputy foreign minister meet