The US official said Ukraine brought forward new ideas and proposals to the Oslo talks on Tuesday, which also involved the leaders of Norway and Finland and European and NATO representatives, and that participants made "meaningful progress" toward a co-ordinated approach to engaging Russia.
The official said the talks covered "key elements of a comprehensive peace framework", including security guarantees for Ukraine, a post-war economic plan and a broader European security architecture.
Witkoff would aim to "create a pathway toward direct trilateral and broader multilateral negotiations", the official said.
Zelenskiy travelled to Oslo seeking to repair relations with Washington, which have sunk to new lows as Trump has courted Moscow. Kyiv has complained that Washington has withheld vital military support and intelligence.
Zelenskiy told a news conference after the meeting and an earlier phone call with US Secretary of State Marco Rubio, that Ukraine was again receiving early warnings of Russian missile attacks.
"Now it works, it's great," he said, adding he and Rubio had discussed supplies of Patriot missile interceptors as well as the satellite-based Starlink system, which Kyiv complained had stopped working when mounted on fast-moving objects such as drones.
President Donald Trump's recent gestures toward Moscow, including a deal to buy Russian diesel and a waiver of new sanctions, sparked bipartisan pushback in the US Congress and concern in European capitals.
Zelenskiy said he had discussed "Article 5-like" security guarantees, referring to the NATO stipulation that an attack on one ally is an attack on all.
"I am thankful to the American side that they underlined again that it will be strong," he said.
Zelenskiy reiterated that Ukraine hoped to discuss key issues on how to end the war during a trilateral meeting of leaders of Ukraine, Russia and the US.
Norway's Prime Minister Jonas Gahr Stoere said the Oslo meeting had been constructive, while Finnish President Alexander Stubb added: "I think the (peace) process is back on track."
Washington has denied deliberately hindering Ukraine's war effort. But Trump has repeatedly rebuked Zelenskiy, and called for him to be replaced.
Trump called on Ukraine to make a deal to settle the war, and said Moscow wanted to get it done.
"Ukraine has to want to settle this war," he told reporters.
Trump suggested Moscow had the upper hand in the war because "Russia is a big machine - they just keep grinding forward, and that's what they've done. They've taken a very large piece of land".
The US has largely stopped providing weapons directly to Ukraine but lets European countries buy US weaponry on Kyiv's behalf under a program known as Prioritised Ukraine Requirements List. It has also provided intelligence and technology that Europe cannot match.
A source familiar with the matter said most weapons deliveries under PURL continued to flow, but US Defense Secretary Pete Hegseth had not approved Ukraine's latest requests for Patriot interceptors.
Rubio acknowledged that a consignment of interceptors bought by European countries for Ukraine may not have been delivered, but denied that the US had changed policy.
"There has not been some deliberate political directive to go out and harm Ukraine," he said on a visit to India.
Hegseth said Washington had not pulled back Ukraine's ability to access Starlink, which is owned by Elon Musk's SpaceX, and appeared to signal that the problem rested with corporate terms of service Kyiv needed to comply with.
Musk has said Starshield, the military-grade version of SpaceX's Starlink communications system, is controlled by the US government and any limits on its use are ultimately up to Trump.
The Wall Street Journal cited US officials and people familiar with the matter as saying that Musk ordered the slowdown after consulting with Trump and other administration officials.
While US ties with Ukraine have deteriorated, Russia has stepped up attacks on Ukrainian cities, particularly targeting power stations and fuel, despite a call from Trump for both sides to spare each other's energy systems.
Russia bombarded cities in western Ukraine overnight, targeting electricity systems and knocking out power across swathes of the country that had previously been spared.
with Reuters and dpa
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