The White House confirmed that Russia is developing an anti-satellite weapon capability. The intelligence was made public by an announcement by Representative Michael Turner (Chair of the House Intelligence Committee), where he called on the Biden administration to declassify the information.
The nature of the threat can be traced all the way back to the Cold War and the dawn of the Space Age, where there were fears of nuclear weapons being stationed in space. The Outer Space Treaty was designed specifically to prohibit such an action. If Russia were to place a nuclear-armed weapon within orbit, they would be violating international law. It is ambiguous whether it would be a nuclear-powered weapon or an actual warhead, but both could be interpreted to be contrary to the prohibitions of the 1967 treaty.
The United States has stated consistently in the past that our satellites are vulnerable to attack. The use of satellites for defense, broadband, and GPS have heightened concerns that Russia will target those systems, as well as U.S. intelligence satellites.