Russia is pursuing a "troubling" anti-satellite weapon (ASAT) that has not been deployed into space and cannot cause "physical destruction" on Earth, U.S. National Security Council spokesperson John Kirby said on Thursday.

Why it matters: Kirby was responding to a cryptic alert sent out on Wednesday by House Intelligence Committee Chair Mike Turner, who described the weapon as a "serious national security threat."

Details: Kirby would not disclose the specific capabilities of the weapon and would not say whether the U.S. has or is developing a defense strategy against it.

• Some media outlets reported Wednesday that the weapon is "nuclear-capable."
• Kirby did not confirm if that description applied to the ASAT but he noted that the term has several meanings. He pointed to nuclear submarines, which can launch nuclear weapons and use nuclear power for propulsion.

What they're saying: Kirby said National Security Advisor Jake Sullivan plans to meet with House leadership and committee chairs to brief them on intelligence and analysis on the potential weapon and would eventually brief the Senate.

• "This is still a capability they are developing," Kirby said. "We're taking this potential threat very, very seriously."
• He said the U.S. has known about the weapon for "many many months, if not a few years." But in recent weeks, the intelligence community was able to "assess with a higher sense of confidence exactly how Russia continues to pursue" the weapon.

The big picture: For decades, Russia has developed weapons that can destroy satellites in low-Earth orbit.

• In 2021, Russia tested a ground-launched missile against one of its satellites in orbit.
• The test generated a cloud of debris that NASA said endangered the International Space Station and its crew, and could have gone on to threaten other satellites.
• The U.S. also has such weapons, but the Biden administration vowed after Russia's 2021 test that it would no longer conduct tests that could generate space debris.

How it works: Anti-satellite weapons are incredibly dangerous not only because they can cripple another nation's military but can destroy systems that modern civilization relies on, like GPS.

• They can do so by generating huge amounts of space debris, or tiny pieces of scrap traveling at tremendous speeds that can punch holes in satellites or spacecraft.
• The amount of debris in orbit has skyrocketed in recent years as more nations — and private companies — have gained space capabilities.
• It's been proposed that too much clutter in Earth's orbit could set off a chain reaction of debris generating more debris that would eventually eliminate our ability to use satellites or explore space.
• It's expected that Earth's orbit is going to become even more crowded in the coming years, potentially setting off competition between countries and generating more debris through accidents, tests or attacks.

Of note: Putting a nuclear weapon in space would violate the 1967 Outer Space Treaty, which Russia observes.

• Satellites powered by nuclear fission reactors have been used in the past, and newer, more powerful designs are believed to be under development in both the U.S. and Russia.
• Such satellites have cause disasters or near disasters in the past. Most notable, the Soviet nuclear satellite Kosmos 954 fell out of orbit and exploded over northern Canada in 1978, spreading radioactive debris across a massive area.

Go deeper ... Next frightening war frontier: Russian nukes in space

Editors note: This story has been updated with additional details.