Ukrainian President Volodymyr Zelenskyy said on Sunday that talks with U.S. representatives on a peace plan to end the Russia-Ukraine conflict have been "constructive" but "not easy," ahead of scheduled meetings with European leaders this week.

"The American representatives know the basic Ukrainian positions," Zelenskyy said in his nightly video address. "The conversation was constructive, although not easy."

Intensive diplomatic efforts have been underway between the relevant parties over the past few days.

Russian President Vladimir Putin said on Thursday that outstanding issues remain regarding the peace plan after his meeting with U.S. envoys at the Kremlin last week.

On Saturday, U.S. and Ukrainian delegations concluded three-day talks in Miami, Florida, focusing on territorial issues and U.S. security guarantees for Ukraine, U.S. online media outlet Axios reported.

Sources told Axios that the discussion on territory was "difficult," as Kyiv has rejected Russia's key demand to withdraw troops from parts of the Donbas, while the United States was trying to develop new ideas to bridge the gap. Another major topic was U.S. security guarantees for Kyiv, on which the parties made "significant progress," the report added.

At the end of the Miami talks, Zelenskyy held a phone call with Trump's special envoy Steve Witkoff and Trump's son-in-law Jared Kushner. Describing the call as "long and substantive," Zelenskyy said on X that Ukraine remains committed to working with the United States "in good faith" to "genuinely achieve peace."

Zelenskyy is expected to meet British, French and German leaders in London on Monday, with further talks planned in Brussels.

Meanwhile, Trump claimed on Sunday that Zelenskyy "isn't ready" to sign off on a U.S-authored peace proposal aimed at ending the crisis.

"I'm a little bit disappointed that President Zelenskyy hasn't yet read the proposal, that was as of a few hours ago. His people love it, but he hasn't," Trump told reporters before taking part in the Kennedy Center Honors event.

Meanwhile, Russia on Sunday welcomed the Trump administration's new national security strategy. Kremlin spokesman Dmitry Peskov said that adjustments made to the strategy are "largely consistent with our vision," RIA Novosti reported.

Peskov said the new U.S. strategy leaves room for hope that joint efforts might result in a peaceful resolution of the Ukraine conflict. "There are phrases opposing confrontation and those favoring dialogue, building good relations. This is what Putin is talking about. This is gratifying, of course," he said.

The White House on Friday released a new national security strategy that paints European allies as weak and aims to reassert America's dominance in the Western Hemisphere.

"It is a core interest of the United States to negotiate an expeditious cessation of hostilities in Ukraine, in order to stabilize European economies, prevent unintended escalation or expansion of the war, and reestablish strategic stability with Russia, as well as to enable the post-hostilities reconstruction of Ukraine to enable its survival as a viable state," the document read.

(With input from Xinhua)