U.S. President Donald Trump said on Thursday that he saw "good signals" toward finalizing a 30-day ceasefire agreement between Russia and Ukraine.

While meeting with NATO Secretary General Mark Rutte at the White House, Trump offered guarded optimism when he was asked by reporters about Russian President Vladimir Putin's statement earlier in the day.

"He (Putin) put out a very promising statement but it wasn't complete," Trump said. "Now we're going to see whether or not Russia's there. And if they're not, it'll be a very disappointing moment for the world."

Earlier on Thursday, Putin told reporters that Russia is "in favor" of the 30-day ceasefire plan proposed by the United States and Ukraine but nuances exist.

Responding to Putin's statement, Ukrainian President Volodymyr Zelensky said the Russian leader is setting many preconditions to delay the ceasefire for as long as possible.

In the Oval Office, Trump said the United States had discussed with Ukraine possible concessions as part of a peace agreement.

"We've been discussing with Ukraine land and pieces of land that would be kept and lost, and all of the other elements of a final agreement," Trump said.

Trump's envoy to the Middle East, Steve Witkoff, has arrived in Moscow to meet with Putin and discuss the ceasefire proposal.

"It doesn't mean anything until we hear what the final outcome is, but they have very serious discussions going on right now with President Putin and others, and hopefully they all want to end this nightmare," Trump said, adding that he hopes to speak to Putin soon.