The top diplomats from the UK, US, France, Germany and Ukraine have postponed a plan to meet in London on Wednesday for high-level talks on how to end Russia's war,
Sky News reports.
Discussions will instead take place among senior officials from the five nations, though the Ukrainian foreign minister is also still due to be in the capital and will hold a bilateral meeting with David Lammy, it is understood.
The downgrading in the level of diplomacy is in contrast with an intensification in the pressure from Donald Trump and his team for Kyiv and Moscow to agree a ceasefire.
A US peace proposal that is due to be discussed in London would see the United States recognise Russia's illegal annexation of Crimea - something rejected by Volodymyr Zelenskyy on Tuesday.
The plan, reported by US media at the weekend, also freezes the frontlines as part of a peace agreement.
Ukraine's allies are hoping to receive security guarantees and reconstruction projects in exchange for any such territorial concessions, it was reported.
The Financial Times claimed that Vladimir Putin has also offered to halt his invasion along the current front lines, which would leave about 20 percent of Ukraine in Russia's hands. It is unclear whether Kyiv would accept such terms.
