Vladimir Putin must leave Ukraine and pay "proper recompense" for his invasion before he can ever return to the international community, Liz Truss has said.
The Prime Minister spoke before launching an update to the integrated review of UK defence and foreign policy, which deals with countering the threat of authoritarian regimes such as Russia and China.
Ms Truss also doubled down on her Tory leadership pledge to increase defence spending to 3% of UK GDP by 2030.
The PM used her first international trip in office to encourage UN allies in New York to keep pressure on Russia and support Ukraine's defence.
Asked by journalists travelling with her if there was a way for Mr Putin to rejoin the international stage, she said: "First Russia needs to leave Ukraine.
"And we need to make sure that there is proper recompense for what has happened in Ukraine and we need to make sure Russia is never again able to threaten countries on its border."
Meanwhile, Ms Truss instructed special adviser Professor John Bew to lead an update into the integrated defence review published in March last year.
To be published by the end of the year, Downing Street said it would ensure the UK can "stand firm against coercion from authoritarian powers like Russia and China".
She will use a speech to the United Nation’s General Assembly on Wednesday to pledge to define a "new era" of "hope and progress".
WATCH: Troops 'play' weapons used against Russia to make music.
"This is a decisive moment in British history, in the history of this organisation, and in the history of freedom," she is expected to say.
During the trip, Ms Truss will pledge that the UK will next year match or exceed the £2.3 billion in military aid to Ukraine given in 2022.
No 10 said she would reiterate the NATO spending commitment for 2030, which the Royal United Services Institute think tank said would cost an extra £157 billion.
Ms Truss met Ukrainian first lady Olena Zelenska and prime minister Denys Shmyal to tour an exhibition titled "Russian Warcrimes" at the Ukrainian Institute of America on Tuesday evening.
The Prime Minister shook her head in despair as she witnessed images including dead children on hospital gurneys and a heavily pregnant woman injured in the shelling of a Mariupol hospital.
"These are the type of crimes we thought had been consigned to history," Ms Truss said.