Rounding the northernmost tip of Russia in his oceangoing tugboat this summer, Capt. Vladimir V. Bozanov saw plenty of walruses, some pods of beluga whales and in the distance a few icebergs.

Iran has started the nuclear reaction at its Bushehr power plant, the Russian company that built the reactor said in a statement on Tuesday that indicated Iran is close to wrapping up work on the site that has dragged on for more than three decades.