The UK has pledged to provide an extra £15 million in overseas aid to help Ukrainian refugees while reports in the US claim Joe Biden is preparing to unveil a further package of military aid for Kyiv worth $800 million (£670 million).
The British package will support as many as 200,000 Ukrainians, both in their home country and in Poland, where the majority of refugees have fled.
The White House could announce its new tranche of aid as soon as Friday, Reuters reported.
Mr Biden would authorize the assistance using his Presidential Drawdown Authority, which allows the president to permit the transfer of excess weapons from US stocks. The White House declined to comment.
Washington has sent billions of dollars in security assistance to the Kyiv government.
Turkish leader Recep Tayyip Erdogan has warned of a nuclear disaster in Ukraine during his first face-to-face talks with Volodymyr Zelensky, the Ukrainian President, since Russia's invasion began, echoing pleas from the UN's chief.
A flare-up in fighting around Europe's largest nuclear facility in Russian-controlled southern Ukraine has sparked urgent warnings from world leaders, and UN chief Antonio Guterres cautioned during talks with Mr Erdogan that any damage to the plant would be akin to "suicide".
"We are worried. We don't want another Chernobyl," Mr Erdogan said during a press conference in the eastern city of Lviv, during which he also assured the Ukrainian leader that Ankara was a firm ally.
"While continuing our efforts to find a solution, we remain on the side of our Ukraine friends."
Mr Guterres said he was "gravely concerned" about the situation at the plant and that it had to be demilitarised, adding: "We must tell it like it is – any potential damage to Zaporizhzhia is suicide."