rouhani-635x357U.S.-Russian tensions over Ukraine spilled over into nuclear talks with Iran Wednesday, with Moscow’s chief envoy at the negotiations warning that his country may take “retaliatory measures” that could hurt attempts to persuade Tehran to cut back on programs that could make atomic arms. The statement, by Deputy Foreign Minister Sergei Ryabkov, appeared to be the most serious threat of reprisal by Moscow for Western sanctions against Russia over its annexation of Ukraine’s Crimea region. Russia is key to attempts to coax Iran into significant long-term curbs of its nuclear program in exchange for relief from U.N. and other sanctions. Iran insists it does not want nuclear arms but is seeking a deal that will result in full sanctions relief. The Russian threat, hours after the latest negotiating round ended, appeared to catch Washington off guard. Days ahead of the meeting, U.S. State Department spokeswoman Jennifer Psaki had said she expects Russia to “remain an active partner” in the talks. During the two-day talks, Western officials involved described Russia’s participation as constructive and unchanged by the Ukraine tensions. MORE