Pete Hegseth says the US president is the "one man in the world capable of convening the parties together to bring peace".
It's after Mr Trump announced he plans to meet Vladimir Putin in Saudi Arabia to discuss ending the war.
Secretary Hegseth is attending today's Nato defence ministers meeting in Brussels.
He said that the Russian aggression on Ukraine was “a factory reset for Nato,” and a moment of “realisation that this alliance needs to be robust, strong, and real.”
“That is why president Trump has called for increased defence spending across the board for Nato, for European countries to recognise this is an urgent, real threat to the continent and this aggression needs to be a wake up call,” he said.
He says that standing up to Russian aggression is “an important European responsibility.”
He praises Trump as “the best negotiator on the planet” for bringing both sides to the table in pursuit of peace.
But he gets confronted by reporters with suggestions that the rapid push to peace and talks with Putin could be seen as amounting to a betrayal of Ukraine.
“There is no betrayal; there is a recognition that the whole world and the US is invested in peace, in a negotiated peace,” he says.
