Russian President Vladimir Putin meets with Yevgeny Balitsky, Moscow-installed governor of the Russian-controlled parts of Ukraine's Zaporizhzhia region (not pictured), amid the Russia-Ukraine conflict, at the Kremlin in Moscow, Russia on Monday. (AP-Yonhap)

President Vladimir Putin on Tuesday signed a revised nuclear doctrine declaring that a conventional attack on Russia by any nation that is supported by a nuclear power will be considered a joint attack on his country.

Putin’s endorsement of the new nuclear deterrent policy comes on the 1,000th day after he sent troops into Ukraine, on Feb. 24, 2022.

It follows US President Joe Biden’s decision to let Ukraine strike targets inside Russia with US-supplied longer-range missiles.

The signing of the doctrine, which says that any massive aerial attack on Russia could trigger a nuclear response, demonstrates Putin’s readiness to tap the country’s nuclear arsenal to force the West to back down as Moscow presses a slow-moving offensive in Ukraine.

Asked whether the updated doctrine was deliberately issued on the heels of Biden's decision, Kremlin spokesperson Dmitry Peskov said the document was published “in a timely manner” and that Putin instructed the government to update it earlier this year so that it is “in line with the current situation.”

Putin first announced changes in the nuclear doctrine in September, when he chaired a meeting discussing the proposed revisions.

Russia's president has previously warned the US and other NATO allies that allowing Ukraine to use Western-supplied longer-range weapons to hit Russian territory would mean that Russia and NATO are at war.

The updated doctrine states that an attack against Russia by a nonnuclear power with the “participation or support of a nuclear power” will be seen as their “joint attack on the Russian Federation.”

It adds that Russia could use nuclear weapons in response to a nuclear strike or a conventional attack posing a “critical threat to sovereignty and territorial integrity” of Russia and its ally Belarus, a vague formulation that leaves broad room for interpretation.

It does not specify whether such an attack would necessarily trigger a nuclear response. It mentions the “uncertainty of scale, time and place of possible use of nuclear deterrent” among the key principles of the nuclear deterrence.

The document also notes that an aggression against Russia by a member of a military bloc or coalition is viewed as "an aggression by the entire bloc," a clear reference to NATO.

At the same time, it spells out conditions for using nuclear weapons in greater detail compared with previous versions of the doctrine, noting they could be used in case of a massive air attack involving ballistic and cruise missiles, aircraft, drones and other flying vehicles.

The wide formulation appears to significantly broaden the triggers for possible nuclear weapons use compared with the previous version of the document, which stated that Russia could tap its atomic arsenal if case of an attack with ballistic missiles.

President Alexander Lukashenko, who has ruled Belarus with an iron hand for more than 30 years and has relied on Russian subsidies and support, has allowed Russia to use his country’s territory to send troops into Ukraine and to deploy some of its tactical nuclear weapons.

Since Putin sent troops into Ukraine, he and other Russian voices have frequently threatened the West with Russia’s nuclear arsenal to discourage it from ramping up support for Kyiv.

Russian hawks have been calling for toughening the doctrine for months, arguing that the previous version failed to deter the West from increasing its aid to Ukraine and created the impression that Moscow would not resort to nuclear weapons. (AP)