MOSCOW — President Biden and President Vladimir V. Putin of Russia agreed to extend the last remaining nuclear arms treaty between their countries, but Mr. Biden confronted his counterpart over the poisoning of a Russian opposition leader and other issues, the White House said.
It was the first call between the leaders of the world’s two nuclear superpowers since Mr. Biden’s inauguration. The New Start treaty, which limits the size of the two countries’ strategic nuclear arsenals, expires on Feb. 5, and the call appeared to seal a last-minute agreement to extend the treaty after the Trump administration declined to do so.
But on a host of other high-stakes matters, Mr. Biden sent the message that he would be taking a harder line on Russia than his predecessor. He raised the poisoning of the Russian opposition leader Aleksei A. Navalny, whose arrest on Jan. 17 sparked protests across the country last weekend, the White House said.
He also spoke to Mr. Putin about what American officials have described as a highly sophisticated hack of American government networks, reports of Russia placing bounties on American soldiers in Afghanistan, and what the White House said was “interference in the 2020 United States election.”
“President Biden made clear that the United States will act firmly in defense of its national interests in response to actions by Russia that harm us or our allies,” the White House statement said. “The two presidents agreed to maintain transparent and consistent communication going forward.”
The Kremlin’s statement on the call confirmed that the two leaders agreed to extend the New Start treaty, but did not mention the sources of tension that the White House said Mr. Biden had raised. Instead, the Kremlin emphasized what it said was a “businesslike and frank” call, echoing hopes in Moscow that Mr. Biden will lead a more professional and predictable administration than that of former president Donald J. Trump.
Mr. Putin, the Kremlin said, “noted that normalizing the relationship between Russia and the United States would be in the interest of both countries and — given their special responsibility for security and stability in the world — of the entire international community.”
The New Start treaty is an Obama-era accord that limits the Russian and American strategic nuclear arsenals to 1,550 warheads and bombs each. It contains a provision for a five-year extension if both sides agree — a move that Mr. Putin has favored but that the Trump administration did not agree to. Mr. Biden decided to seek the five-year extension shortly after he took office last week, arguing that doing so could prevent a nuclear arms-race at a time of competition and confrontation with Moscow around the world.
Mr. Putin and Mr. Biden “voiced their satisfaction” about diplomatic steps taken earlier in the day to exercise the extension, the Kremlin said.
“In the coming days, both sides will finish the procedures necessary to assure the continued functioning of this important international legal mechanism to place mutual limits on nuclear-missile arsenals,” the Kremlin said.