The two United Nations Security Council members are pursuing "anti-satellite weapons as a means to reduce U.S. and allied military effectiveness," the report said, reflecting input from organizations including the FBI, the CIA, and the National Security Agency.
Anti-satellite weapons, which include ballistic missiles, are designed to damage space-based systems. They are a major element of what is known as counterspace technology, or hardware and software that aim to hinder adversaries in outer space.
"We assess that, if a future conflict were to occur involving Russia or China, either country would justify attacks against U.S. and allied satellites as necessary to offset any perceived U.S. military advantage derived from military, civil, or commercial space systems," the report said.
"Of particular concern, Russia and China continue to launch 'experimental' satellites that conduct sophisticated on-orbit activities, at least some of which are intended to advance counterspace capabilities," it continued.
President Donald Trump's administration has criticized Moscow for dangerous military activities, but the White House has yet to impose long-awaited sanctions on Putin's government. Several of Trump's former aides are under investigation for alleged collaboration with the Kremlin, and a special counsel is investigating whether the Trump campaign colluded with Russia during his presidential run.
Beijing's trade and currency practices, meanwhile, remain one of Trump's major complaints.