Il CSIS ha pubblicato un report che analizza il ruolo della Russia e della Cina nella competizione strategica tra Stati Uniti ed Iran.
Facilmente sintetizzato in questo passaggio:

China and Russia are key players in US-Iranian strategic competition. As major world powers and permanent members of the UN Security Council, China and Russia play an important role in shaping sanctions and other aspects of international action in dealing with Iran’s nuclear program. Leaders in Moscow and Beijing focus on the influence, security and economic gains to their respective leaderships, and pursue international relationships from that standpoint. At present, external pressure from the US and its allies is not able to make either China or Russia give up all ties to Iran, and they manipulate such ties to Iran as a bargaining chip in dealing with the US, as well as the European and Arab Gulf states.
Both countries seek to maximize the benefits they can gain from the ongoing competition by refusing to commit to either player. Both nations have an interest in preventing or at least forestalling open hostility that will upset this balancing act, as any conflict could have an impact on their economies and seek to use their support of either side to advance their own positions.