Moscow said Tuesday that ally China had every right to take measures to protect its sovereignty and called U.S. House Speaker Nancy Pelosi's Taiwan visit a "clear provocation".
"The Chinese side has the right to take necessary measures to protect its sovereignty and territorial integrity over the Taiwan issue," the Russian foreign ministry said. Moscow called Pelosi's visit "a clear provocation" aimed at containing China.
China's military said it would "launch a series of targeted military actions in response" to Pelosi's visit.
"We urge Washington to refrain from actions that undermine regional stability and international security and recognize the new geopolitical reality, in which there is no longer room for American hegemony," the Russian foreign ministry said.
Earlier Tuesday Russia expressed full solidarity with China.
Kremlin spokesman Dmitry Peskov said Pelosi's visit was leading to an "increase in tension" in the region and accused Washington of choosing "the path of confrontation".
"We want to emphasise once again that we are absolutely in solidarity with China, its attitude towards the problem is understandable and absolutely justified."
Russian foreign ministry spokeswoman Maria Zakharova also accused the United States of being provocative over the potential visit.
"Washington is bringing destabilisation to the world. Not a single resolved conflict in recent decades, but many provoked ones," she said on social media.
Faced with unprecedented sanctions over its military intervention in pro-Western Ukraine, Russia has sought closer ties with China.
Pelosi, second in line to the presidency, is the highest-profile elected U.S. official to visit the island of Taiwan in 25 years and Beijing has made clear that it regards her presence as a major provocation, setting the region on edge.
China considers self-ruled, democratic Taiwan its territory.
Moscow's assault on Ukraine has heightened fears that Beijing might similarly follow through on threats to annex its much smaller and outgunned neighbour.