In launching an audacious drone attack on airfields and warplanes deep inside Russia, Ukraine is continuing to change the way wars will be conducted in the 21st century, according to U.S. officials and military analysts.

American and European security officials said battle damage assessments were still coming in from the attacks, which took place Sunday, but they estimated that as many as 20 Russian strategic aircraft may have been destroyed or severely damaged, dealing a serious blow to Russian’s long-range strike capabilities.

Officials said Russia’s losses included six Tu-95 and four TU-22M long-range strategic bombers, as well as A-50 warplanes, which are used to detect air defenses and guided missiles.

The attack, known as Operation Spider’s Web, hurt Moscow’s prized strategic capabilities. But just as significantly, it demonstrated Ukraine’s ability to strike nearly anywhere in Russia, and to destroy warplanes costing $100 million or more with drones with price tags as low as $600, according to one U.S. defense official.

U.S. officials said that Ukraine did not give the Trump administration advance notice that forces with Ukraine’s Security Service, or S.B.U., were planning the attack, which targeted several air bases inside Russia, including one in Siberia.