British Prime Minister Liz Truss on Wednesday accused Russian President Vladimir Putin of making ?saber-rattling threats? to cover his failed invasion of Ukraine, as she prepared to tell the United Nations that its founding principles were fracturing because of aggression by authoritarian states.

In her debut speech to the U.N. General Assembly on Wednesday night, Truss will call the war in Ukraine a battle for ?our values and the security of the whole world,? and extol the late Queen Elizabeth II as a symbol of everything the U.N. stands for.

The text of the speech was released in advance by Truss? office.

Responding to a statement from Putin that he was mobilizing reservists and would use everything at his disposal to protect Russia ? an apparent reference to his nuclear arsenal -- Truss accused the Russian leader of ?desperately trying to justify his catastrophic failures.?

?He is doubling down by sending even more reservists to a terrible fate,? the speech said. ?He is desperately trying to claim the mantle of democracy for a regime without human rights or freedoms. And he is making yet more bogus claims and saber-rattling threats."

?This will not work. The international alliance is strong ? Ukraine is strong,? said Truss, who addressed the U.N. on the same day Ukrainian President Volodymyr Zelenskyy addressed the global gathering by video.

In a speech outlining her view of foreign policy in a world turned upside down by Russia?s invasion, Truss spoke of the queen, whose funeral on Monday was attended by many of the world leaders now gathered at the United Nations.

She said the queen ?symbolized the postwar values on which this organization was founded.? She said the monarch, who died this month after 70 years on the throne, ?transcended difference and healed division.?

Truss referred to a speech to the U.N. by the queen in 1957, in which Elizabeth said ?the peoples of the world expect the United Nations to persevere in its efforts? to end conflict and crisis.