VIENNA — Talks on a permanent nuclear agreement with Iran resumed in Vienna on Tuesday, heavily shadowed by the Ukraine crisis between the West and Russia. But European and American officials said their differences with the Kremlin had no effect on the unified position they all take aimed at ensuring the Iranians can never make atomic bombs.

Iran’s delegation to the two-day talks here made no public mention of the East-West crisis over the fate of Ukraine’s Crimean Peninsula, which the Russian government annexed on Tuesday in defiance of Western condemnation and economic sanctions. Western diplomats and proliferation experts have said they feared the crisis would create schisms that Iran could exploit among the so-called P5-plus-1 countries negotiating with Iran, which are the five permanent members of the United Nations Security Council — Britain, China, France, Russia and the United States — plus Germany.

Michael Mann, a spokesman for Catherine Ashton, the European Union’s top foreign policy official, who is the lead negotiator for the P5-plus-1 group, told reporters that he had not seen “any negative effect” on the talks attributable to the Ukraine crisis.