Kerry's comments at a news conference with German Foreign Minister Guido Westerwelle came ahead of a preparatory meeting in Geneva next week on a US-Russian bid for a peace conference on Syria.
"In Geneva, we will test who is serious. Are Russians serious about pushing for that? I believe they are. President (Vladimir) Putin said they are, (Foreign Minister) Sergei Lavrov has said it and they are trying to organize.
"Now, it is not helpful to have the S-300 transferred to the region while you are trying to organize this peace and create peace," he said.