Ukraine's Volodymyr Zelensky has said he and Donald Trump discussed sanctions against Russia, defence cooperation and drone production ahead of a visit to Moscow by US envoy Steve Witkoff.
Thanking Trump for "productive" talks on Tuesday, Zelensky claimed that Moscow was particularly "sensitive" to the prospect of sanctions.
Trump has previously stated that if Russia fails to agree a ceasefire with Ukraine by Friday it will face hefty sanctions or see secondary sanctions imposed against all those who trade with it.
Witkoff is thought to be travelling to Russia tomorrow or Thursday and is expected to meet Vladimir Putin.
The Kremlin has mostly skirted Trump's sanctions threat, though spokesman Dmitry Peskov noted last week that the Russian economy had "developed a certain immunity" to sanctions due to being under them for so long. Trump has also admitted that he did not know whether sanctions "bothered" Putin.
The US president may be hoping that Russia's trading partners will be sufficiently inconvenienced by the tariffs that they will choose to pivot away from buying Moscow's oil - ultimately making a dent in the revenue the Kremlin needs to continue waging its war on Ukraine.
On Monday Trump said he would impose hefty new tariffs on India, a major buyer of Russian oil, accusing it of not caring "how many people in Ukraine are being killed by the Russian War Machine". The Kremlin said "attemps to force countries to cut trade relations with Russia" were "illegal".
In his Telegram post Zelensky said he and Trump had also talked about the "increased brutality" of Russian strikes on Ukraine.
The US president has previously referenced Moscow's repeated attacks on Ukrainian cities, signalling irritation that the bombings often follow "nice" phone conversations between himself and Putin.
Only last February Zelensky was asked to leave the White House after a disastrous meeting in which the US president accused him of not being thankful enough for US aid and of "gambling with World War Three".
The two men have gradually repaired their relationship. In July Trump said the US would sell "top-of-the-line weapons" to Nato members which would then pass them on to Kyiv - and this week it was announced that Denmark, Norway, the Netherlands and Sweden would be the first countries to buy weapons from the US under this scheme.
Their combined contributions will amount to more than $1bn and will go towards air defence equipment and ammunition.
Danish Defence Minister Troels Lund Poulsen said speed was "absolutely critical" and that Denmark would be willing to consider additional funding later.
More than three years on from Russia's full-scale invasion, Ukrainian cities continue to come under heavy bombardment and regular drone attacks. Over the last day six people were killed across eastern Ukraine, authorities said.
Before taking office Trump repeatedly said he would be able to end the conflict within a day - and it was at his behest that Russia and Ukraine sat down for ceasefire talks for the first time last May.
But the discussions failed to bring the two sides any closer to peace and the US president has appeared increasingly impatient with the lack of progress.
Despite Trump’s looming deadline, Vladimir Putin last week poured cold water on any hopes of a swift, long-term ceasefire with Ukraine. Although he said he viewed talks with Kyiv "positively," he also noted that "all disappointments arise from inflated expectations".