The Kremlin said on Monday that any US decision to allow Ukraine to fire US missiles deep into Russia would mean it was directly involved in the conflict, which it accused Joe Biden's administration of escalating.
Russia has been telling the West for months how it would interpret such a decision, and that it would raise the risk of a confrontation with the US-led NATO alliance.
When asked about reports by The New York Times and Reuters that Biden's administration had made the decision on long-range strikes, Kremlin spokesman Dmitry Peskov said the reports were not based on any official statement.
"If such a decision was indeed formulated and brought to the Kyiv regime, then this is a qualitatively new round of tension and a qualitatively new situation from the point of view of US involvement in this conflict," Peskov said.
President Vladimir Putin had expressed Russia's position clearly when speaking in St. Petersburg in September, he said.
Putin said on Sept 12 that Western approval for such a step would mean "the direct involvement of NATO countries, the United States and European countries" in the conflict, because NATO military infrastructure and personnel would have to be involved in the targeting and firing of the missiles.
"It's obvious that the outgoing administration in Washington intends to take steps to continue fueling the fire and provoke a further escalation of tensions," Peskov said.
Reuters reported the Biden administration's decision on Sunday, citing two US officials and a source familiar with the decision. The New York Times also reported the decision.
The move comes before US President-elect Donald Trump takes office on Jan 20 and follows months of pleas by Ukrainian President Volodymyr Zelensky to allow Ukraine's military to use US weapons to hit Russian military targets far from its border.
Zelensky said on Sunday the missiles would "speak for themselves".
"Today, many in the media are saying that we have received permission to take appropriate actions," he said. "But strikes are not made with words. Such things are not announced."
Vladimir Dzhabarov, first deputy head of the Russian upper house's international affairs committee, said Washington's decision could lead to "World War III".
In Washington, it is not clear if Trump will reverse Biden's decision when he takes office. Trump has long criticized the scale of US financial and military aid to Ukraine and has vowed to end the conflict quickly, without explaining how.
One of Trump's closest foreign policy advisers, Richard Grenell, criticized the decision. "Escalating the wars before he leaves office," he said on X, responding to the news.
