TEHRAN  Thirty-six years after construction began under the shah, Iran finally opened its first nuclear power plant at a ceremony on Saturday.

Attended by senior officials from Iran and Russia, which helped build the plant, the ceremony marked the beginning of the transfer of low-enriched uranium fuel rods from a storage site into the plant. Officials of both countries said that Saturday’s events signified the opening, not the startup, of the plant near Bushehr, in southern Iran.

The plant itself is not controversial, because the Russians plan to provide fuel for it and to remove spent fuel that could be used to make weapons. But the opening was sure to upset United States diplomats, who had encouraged Russia to delay it as a way to add to economic sanctions imposed on Iran because of its refusal to cease enrichment of uranium at its other nuclear facilities. Although Iran denies that it is using its civilian nuclear program to mask a plan to build a bomb, many Western countries are dubious.

The chief of Russia’s Rosatom state nuclear power company, Sergei Kiriyenko, speaking to members of the news media in an amphitheater of the Bushehr complex, took pains to emphasize, as Russians have for years, that the plant complied with the requirements of the International Atomic Energy Agency.