US envoy Steve Witkoff has arrived in Saint Petersburg to meet Russian President Vladimir Putin, following what US Secretary of State Marco Rubio described as "positive" talks with Ukrainian President Volodymyr Zelenskyy.
The visit comes amid efforts to ease tensions between US President Donald Trump and Zelenskyy over Russia's war on Ukraine.
Following talks with Witkoff in Oslo, Zelenskyy thanked Washington on Tuesday for resuming intelligence sharing on Russian strikes.
"We are thankful that intelligence works," Zelenskyy told reporters in Oslo, describing the early warnings as "very, very important for our people, for children, adults, civilians" when ballistic missiles were about to strike.
The latest talks follow days of tensions between Kyiv and Washington.
Zelenskyy and Trump have endured a volatile relationship since the US president began his second term in January last year, but it has soured further in recent weeks after Trump struck a diesel deal with Putin and criticised the impact of Ukrainian strikes on Russia's energy sector on global fuel prices.
Speaking at the White House on Tuesday, Trump renewed calls for Zelenskyy to "make a deal" with Russia, as Moscow intensifies its strikes on Ukraine ahead of winter.
Meanwhile, Zelenskyy has accused Washington of delaying deliveries of interceptor missiles already paid for by European countries, with some shipments reportedly awaiting US approval.
The Ukrainian president also insisted that Kyiv must be involved in any negotiations concerning its future.
"If there are issues about Ukraine, our future, it can be acceptable only when we are at the table of negotiations," Zelenskyy said on Tuesday.