VIENNA (AP) — U.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.