WASHINGTON — President Joe Biden and President Vladimir Putin of Russia avoided a renewed arms race Tuesday when they formally agreed to extend the last remaining nuclear arms treaty between their countries. But White House officials said Biden also confronted the Kremlin leader over the poisoning of an opposition activist and a hacking of government and private computer networks in the United States.

It was the first call between the leaders of the world’s two largest nuclear powers since Biden’s inauguration. But it was being watched as much for its tone as its substance: Biden vowed during the transition to make Russia “pay a price” for the hacking, and his administration, in its opening hours, demanded the release of Alexei Navalny, whose arrest on Jan. 17 prompted protests last weekend across Russia that resulted in more than 3,000 arrests.

The call was, in essence, the opening act of what promises to be a deeply adversarial relationship between the two leaders, and most likely the sharpest turn in American foreign policy since President Donald Trump left office one week ago.

American intelligence agencies, led by the CIA, assessed before the 2020 election that Putin had a clear preference for the reelection of Trump, who, during his four years in office, treated the Russian leader with remarkable deference. Biden, in contrast, had repeatedly called Putin a “KGB thug” and mocked Trump as “Putin’s puppy.” Putin, for his part, had chastised Biden for his “sharp anti-Russian” language.

The call came at the request of the Russians at a moment when Biden is receiving congratulatory calls — all determined to get off on a good foot with a new administration — from many national leaders.

But there was an immediate need: The New START agreement, which limited the size of the two countries’ strategic nuclear arsenals, expires on Feb. 5.

On Monday night, the countries exchanged diplomatic notes to extend the treaty for five years, the maximum allowed in its text. Trump had initially declared that he would not extend it unless China also joined. The Chinese immediately rejected the idea.