WASHINGTON 

President Donald Trump said Monday that he thinks the US and Europe will be able to reach an agreement to provide Ukraine with security guarantees as part of a potential peace deal to end Russia's war.

"I'm optimistic that collectively, we can reach an agreement that would deter any future aggression against Ukraine, and I actually think there won't be," he said while hosting Ukrainian President Volodymyr Zelenskyy and other European leaders at the White House.

"I think that the European nations are going to take a lot of the burden. We're going to help them, and we're going to make it very secure," he added.

Trump also said the leaders would be discussing territorial swaps between Russia and Ukraine "taking into consideration the current line of contact. That means the war zone."

The US president had earlier told reporters during an Oval Office meeting with Zelenskyy that a ceasefire is "unnecessary," but changed tune roughly an hour later when European leaders joined the talks.

"All of us would obviously prefer an immediate ceasefire while we work on a lasting peace. And maybe something like that could happen. As of this moment, it's not happening, but President Zelenskyy and (Russian) President (Vladimir) Putin can talk a little bit more about that," he said.

Trump was optimistic that a trilateral summit with himself, Zelenskyy and Putin will be arranged after Monday's White House talks. 

"I think when we set that up, when we do, I think it's going to be when, not if, I think you're going to see some very, really positive moves," he said. "I know there's over 1,000 prisoners, and I know they're going to release them, they're going to release them very soon, like immediately, which I think is great. We're going to set that up today, after this meeting."

Trump said he would be meeting with European leaders in the Oval Office after they conclude their talks for a previously unscheduled sit-down, a potential sign that the talks are progressing well.