MOSCOW — Russian President Vladimir Putin met with President Donald Trump ’s special envoy tasked with negotiating an end to Russia’s war in Ukraine, as well as his son-in-law, for a "constructive" five-hour meeting Tuesday, but more work needs to be done, Yuri Ushakov, a foreign policy adviser to Putin, said in a video the Kremlin posted online.

The presidents of Ukraine and Russia are expected to be briefed this week on outcomes of Sunday's U.S.-Ukraine talks.

Russian President Vladimir Putin threatened on Tuesday to sever Ukraine's access to the sea in response to drone attacks on tankers of Russia's "shadow fleet" in the Black Sea.

Russian President Vladimir Putin said that a US plan to end the war in Ukraine could “form the basis for future agreements” but renewed threats to seize more territory by force unless Kyiv withdraws.

Russian President Vladimir Putin has claimed without evidence that Russian forces have taken control of Ukrainian cities Pokrovsk and Vovchansk.

European officials, who were not included in the talks, said at a NATO meeting in Brussels that Russia appears to be inflexible in the negotiations.

Kremlin aide Yuri Ushakov said on Wednesday that Russia's recent battlefield progress in Ukraine had what he described as a positive impact on peace negotiations held with U.S. envoys in Moscow a day earlier.