The Russian President Vladimir Putin lowered on Tuesday the threshold for Russia to use its nuclear weapons. This follows U.S. president Joe Biden’s decision to allow Ukraine to strike targets within Russian territory using longer-range missiles supplied by America.

The new doctrine permits a possible nuclear response from Moscow to any conventional attack by a nation supported by a nuclear-armed power on Russia.

The Russian Defense Ministry reported that Ukraine launched six ATACMS-made in the United States missiles at a military base in Russia’s Bryansk Region, which borders Ukraine. It added that air defenses destroyed five of them while damaging one. Ukraine’s military said the strike was on a Russian ammunition storage facility.

The doctrine envisages a possible Russian nuclear response to a conventional attack, but it is written in a way that avoids any firm commitment by Putin to use nuclear weapons.

Sergey Lavrov, the Russian Foreign Minister, said that the Ukrainian strike on Bryansk was an escalation. He urged the U.S. as well as other Western allies study the modernized doctrine of nuclear weapons.

“If long-range missiles from Ukraine are used against Russian territory, that will mean they are controlled American military experts. We will view that as an entirely new phase of Western war against Russia and will respond accordingly,” Lavrov stated on the sidelines the G20 in Brazil meeting without providing any further details.

The document’s approval shows Putin’s willingness to use his nuclear arsenal in order to force the West into submission as Moscow continues its slow-moving offensive against Ukraine, as the war enters its 1,000th day.

Dmitry Peskov, the Kremlin’s spokesman, answered yes when asked Tuesday if an attack by the U.S. using longer-range missiles against Ukraine could trigger a possible nuclear response. He cited the doctrine provision which allows for a nuclear strike after a conventional attack that poses a serious threat to “Russian sovereignty and territorial integrity” and Belarus.

Peskov, when asked if the doctrine update was issued deliberately to follow Biden’s decision he said that the document was “published in a timely fashion” and that Putin had instructed the government earlier this year to update it so that it was “in line with current situation.”

Putin announced the first changes to the nuclear doctrine back in September when he presided over a discussion on the revisions. He warned the U.S., and other NATO allies in the past that allowing Ukraine use longer-range weapons supplied by Western countries to strike Russian territory would be a sign that Russia and NATO were at war.

Washington has allowed Ukraine to use longer-ranged weapons against targets in Russia, after announcing that thousands of North Korean soldiers were deployed to the Russian region Kursk to combat an invasion by Kyiv’s forces.

Matthew Miller, a spokesman for the U.S. State Department, said that he was “unfortunately not surprised” by the Kremlin’s comments in relation to the publication of the new, revised document. He added that, since the beginning of the war, Russia had sought “to coerce and intimidate Ukraine as well as other countries throughout the world, through irresponsible nuke rhetoric and behavior.”

He said that Washington had not found any reason to “adjust our own nuclear position, but we will keep calling on Russia to cease bellicose and reckless rhetoric.”

An official of the U.S. National Security Council who requested anonymity and was not authorized by Washington to make public comments, said that the arrival of North Korean soldiers in Ukraine to participate in combat operations was a significant escalation of Moscow’s actions that required a response.

Keir starmer, the British Prime Minister, denounced “the irresponsible language coming from Russia” and said that it would not deter his support for Ukraine.

“We are now in Day 1,000 of the conflict.” He said that 1000 days of Russian aggression and 1,000 days of sacrifices were made in Ukraine. “We have been with Ukraine since the beginning. “I’ve been repeating my message in a clear way that we must ensure Ukraine has everything it needs for as long as necessary to win this battle against Putin.”

Annalena Bärbock, the German Foreign Minister, said that in Warsaw her country will not be intimidated. She added that Germany made the mistake in the past of cowering before Moscow’s aggression but it would not make the same mistake again.

Radek Sikorski, Poland’s foreign minister in Warsaw described the Russian nuclear doctrine revision as a tacit acknowledgment that Moscow’s conventional forces were weaker than NATO.

According to the updated doctrine, an attack by a non-nuclear country against Russia with “participation” or “support” from a nuclear nation will be viewed as a “joint assault on the Russian Federation.”

The document says that any massive air attack on Russia may trigger a nuclear reaction, but it avoids making any commitments and mentions “uncertainty about the scale, the time and the place of a possible nuclear deterrent use” as one of the key principles for nuclear deterrence.

The document notes that an aggression against Russia committed by a member or coalition of a military alliance is considered “an attack by the entire group,” which is a direct reference to NATO.

It also outlines the conditions for the use of nuclear weapons more clearly than previous versions, noting that they could be used if a massive air strike was launched using ballistic missiles, cruise missiles, aircrafts, drones and flying vehicles.

The document’s prior version stated that Russia could use its nuclear arsenal in the event of a ballistic missile attack.

Alexander Lukashenko has been ruling Belarus with iron fist for over 30 years. He has also relied on Russian support and subsidies. Now, he has allowed Russia use the territory of his country to send troops to Ukraine and deploy some tactical nuclear weapons.

Since Putin’s troops entered Ukraine, he has repeatedly threatened the West to stop increasing its support for Kyiv by threatening it with Russia’s arsenal of nuclear weapons.

Russian hawks have been calling for a tougher doctrine for several months. They claim that the old version did not deter the West to increase its aid for Ukraine, and gave the impression that Moscow wouldn’t resort to nuclear weapons.