US President Joe Biden has cleared Kyiv to use long-range American missiles against military targets inside Russia, a US official told AFP, prompting China on Monday to call for a “cooling down of the situation.”

The official, speaking on condition of anonymity, was confirming reports from The New York Times and The Washington Post that the major policy shift — long demanded by Ukraine — was in response to North Korea deploying troops to help Moscow’s war effort.

Ukrainian President Volodymyr Zelensky has long pushed for authorization from Washington to use the powerful Army Tactical Missile System, known by its initials ATACMS, to hit targets inside Russia.

There was no immediate reaction to the news from the Kremlin.

The head of Russian parliament’s defense committee in the lower house Duma, Andrei Kartapolov, was quoted by the state Ria Novosti agency as saying that “absolutely nothing will change the course of the operation” in Ukraine.

Ukraine’s staunch supporter Poland was among the first to welcome the development.

“With the entry into the war of North Korea troops and (Sunday’s) massive attack of Russian missiles, President Biden responded in a language that (Russian President) V.Putin understands,” Foreign Minister Radoslaw Sikorski posted on X.

“The victim of aggression has the right to defend himself,” he added.

China, which has presented itself as a neutral party to the Ukraine war, urged a peaceful settlement.

“An early ceasefire and a political solution serve the interests of all parties,” foreign ministry spokesman Lin Jian told a regular briefing, when asked about the US decision.

“The most urgent thing is to promote the cooling down of the situation as soon as possible,” he said.

Zelensky’s response, in his evening address Sunday, was more muted.

“Today, there are many media reports that we have received permission to take appropriate actions,” he said.

“But strikes are not made with words. Such things are not announced. The missiles will speak for themselves. Definitely.”

News of Biden’s decision came hours after Ukraine announced nationwide emergency power restrictions from Monday after Russia launched a massive attack that killed 11 civilians and further damaged the country’s already fragile energy grid as winter approaches.