New York, Sept. 11 -- The five permanent members of the UN Security Council clashed on Thursday over the legal status of international sanctions on Iran, with Russia and China challenging the validity of efforts to revive UN sanctions under the 2015 nuclear deal's "snapback" mechanism.

The dispute erupted during a high-stakes council session after Russia sought to block a scheduled briefing on the 1737 Sanctions Committee, arguing that the legal basis for the committee and the sanctions regime had expired.

The snapback mechanism, established under the 2015 Joint Comprehensive Plan of Action (JCPOA) and endorsed by Security Council Resolution 2231, was designed to restore UN sanctions if Iran was found to be in significant breach of its nu...