Mahmood Shoori of Iran's Center for Strategic Research offered two reasons behind the secrecy in an interview with Radio Sputnik.
"Firstly, the final round of bilateral consultations is still underway. Any leaks might damage the agreement. Secondly, the Russians are very restrained in their comments and, as far as I understand, do not want to put the cart before the horse," he said.
Shoori added that Iran would likely receive the S-300PMU-1 or S-300PMU-2 but this is still up for discussion.
When Russia fulfills its obligations under the new deal, Moscow's "positive image in the eyes of the Iranians will undoubtedly improve," he concluded.
Russian President Vladimir Putin lifted the S-300 delivery ban in April 2015, shortly after the P5+1 group of international negotiators and Iran reached a framework nuclear agreement to remove all economic sanctions against Tehran in exchange for its pledge to ensure that all nuclear research in the country will be for peaceful purposes.
