Secretary of State Marco Rubio said on Sunday said the details of the negotiations to end the Russia-Ukraine war will need to be determined by the two countries, stressing that the U.S. is not in a position to accept the terms of a peace deal to end a war that it is not directly involved in.

The U.S. merely serves as a mediator to try and bring the parties closer together before they meet themselves, Rubio said in an interview on CBS News’s “Face the Nation.”

"The United States is not in a position to accept anything or reject anything, because ultimately, it's up to the Ukrainians. They're the ones that Russia has to make peace with, Ukraine with Russia," Rubio told host Margaret Brennan.

Rubio touted President Trump’s progress in his summit with Russian President Vladimir Putin on Friday but stressed that concessions will need to be made by both parties if there is any hope of a diplomatic end to the war.

A potential deal will come down to "what Ukraine can accept and what Russia can accept. They both have to accept it, otherwise there won't be a peace deal,” Rubio said.

“In order for there to be a peace deal — this is just a fact — we may not like it, it may not be pleasant, it may be distasteful, but in order for there to be an end of the war, there are things Russia wants that it cannot get, and there are things Ukraine wants that it's not going to get,” Rubio said in the interview.

“Both sides are going to have to give up something in order to get to the table, in order to make this happen. That's just the way it is,” he continued. “And I mean, the sooner we accept that, that's the reality.”

Ukrainian President Volodymyr Zelensky and other European leaders will meet with Trump at the White House on Monday to discuss the Friday meeting with Putin and next steps in the negotiations.