The cellphones known as 5G, or fifth generation, represent the vanguard of a wireless era rich in interconnected cars, factories and cities. Whichever nation dominates the new technology will gain a competitive edge for much of this century, according to many analysts. But a television network a few blocks from the White House has been stirring concerns about a hidden flaw.

“Just a small one,” a TV reporter told her viewers recently. “It might kill you.”

The Russian network RT America aired the segment, titled “A Dangerous ‘Experiment on Humanity,’” in covering what its guest experts call 5G’s dire health threats. U.S. intelligence agencies identified the network as a principal meddler in the 2016 presidential election. Now, it is linking 5G signals to brain cancer, infertility, autism, heart tumors and Alzheimer’s disease — claims that lack scientific support.

Yet even as RT America, the cat’s paw of Russia’s president, Vladimir Putin, has been doing its best to stoke the fears of American viewers, Mr. Putin, on Feb. 20, ordered the launch of Russian 5G networks in a tone evoking optimism rather than doom.

“We need to look forward,” he said, according to Tass, the Russian news agency. “The challenge for the upcoming years is to organize universal access to high-speed internet, to start operation of the fifth-generation communication systems.”