The decision by the United States to allow Ukraine to use long-range American missiles against targets in Russia marks a “new round of tension” in the war, the Kremlin said Monday.

“If such a decision was really formulated and brought to the attention of the Kyiv regime, then, of course, this is a qualitatively new round of tension and a qualitatively new situation in terms of the involvement of the United States in this conflict,” spokesperson Dmitry Peskov told Russian media.

The comments come after it was widely reported that U.S. President Joe Biden authorized Ukraine to use U.S.-supplied long-range missiles, also known as the Army Tactical Missile System or ATACMS, for strikes on Russian territory.

The move marks a major shift in U.S. policy after the Biden administration’s long-standing refusal to agree to Ukraine’s request for authorization to use the missiles to hit targets outside its own borders.

Russia, for its part, has been using Iranian killer drones and North Korean missiles against Ukraine during President Vladimir Putin’s lengthy full-scale invasion, according to reports by research groups and intelligence services.

Biden’s approval came in response to Russia’s use of North Korean troops in the war, The New York Times reported.

However, Biden’s decision to allow strikes into Russia “will not change” the balance of power on the battlefield, a high-level French military official told reporters Monday.

It “can slow things down, but not stop them,” he added. That’s because, overall, the Ukraine war is also an “industrial war” in which whoever produces the most weapons in the long run is most likely to win. “Even without the North Koreans, Russia has more people on the front line,” the top official also said.

Ukrainian President Volodymyr Zelenskyy reacted Sunday to the missile reports, saying: “Today, there’s a lot of talk in the media about us receiving permission for respective actions.

“But strikes are not carried out with words. Such things are not announced. Missiles will speak for themselves,” he added.

“This is a very big step toward the beginning of the third world war,” said Vladimir Dzhabarov, first deputy chairman of the Russian upper house’s international affairs committee on Sunday, adding that Moscow's response will be immediate.

Earlier in September, Putin had warned Western countries against any such move, saying it would be tantamount to NATO’s “direct participation” in the war.

Laura Kayali contributed to this report.