In a pointed warning to the West, Russian President Vladimir Putin said any nation’s conventional attack on Russia supported by a nuclear power will be considered a joint attack on his country.

Putin's announcement came as the Biden administration announced $375 million in additional security assistance to Ukraine, including air-to-ground weapons, munitions for rocket systems and artillery, armored vehicles and anti-tank weapons.

The warning came at a meeting of Russia’s Security Council, with Putin announcing revisions to the country's nuclear doctrine.

Putin said a revised version of the document states that an attack against his country by a nonnuclear power with the "participation or support of a nuclear power" will be seen as a "joint attack on the Russian Federation."

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Russian President Vladimir Putin listens during a meeting at the Novo-Ogaryovo estate near Moscow. (Gavriil Grigorov/Pool/AFP via Getty Images)

Putin emphasized that the revised doctrine spells out conditions for using nuclear weapons in greater detail, noting they could be used in case of a massive air attack.

"Conditions for Russia’s move to use nuclear weapons are clearly stated" in the revisions, he said.

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"We will consider such a possibility when we receive reliable information about a massive launch of air and space attack assets and them crossing our state border," Putin added, citing "strategic and tactical aircraft, cruise missiles, drones, hypersonic and other flying vehicles."

Ukrainian President Volodymyr Zelenskyy addresses the 79th United Nations General Assembly at U.N. headquarters in New York City. (Reuters/Mike Segar)

The Kremlin's revision of its nuclear response doctrine has opened the door for a major nuclear power to loosen its declaratory policy, which is "never good," one expert warned.

"Regardless of whether you think this is a bluff or not, it’s never good when a major nuclear power loosens the conditions for nuclear use in its declaratory policy," Samuel Charap, senior political scientist at RAND, said in a post on X.

The $375 million package for Ukraine was announced by U.S. Secretary of State Antony Blinken late Wednesday.

President Biden addresses the U.N. General Assembly earlier this week in New York City. (Getty Images)

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"The United States is committed to Ukraine’s defense against Russia’s brutal aggression," Blinken said in a statement. "We will deploy this new assistance as quickly as possible to help Ukraine protect its territory and its people."

Ukrainian President Volodymyr Zelenskyy is scheduled to meet with President Biden and Vice President Harris in Washington Thursday to discuss allowing his troops to use long-range weapons to strike deeper into Russia.

The Associated Press contributed to this report.