According to the intermediary, former Israeli PM Bennet, it was the Brits, primarily, who advised the Ukies to keep fighting, with the US vacillating.
Boris Johnson went to Ukraine to torpedo the cease fire at the last moment
One of the things that Boris promised Ukraine was hundreds of billion of dollars in direct American military and financial aid to support Ukrainian the fight -which is what convinced Zelensky to walk away from the signing of the agreement
The Biden Administration wanted a proxy war for a lot of reasons, not the least of which was an excuse to blame Russia for the Biden induced induced inflation and sky high gas prices
Remember “The Putin Price Hike” mantra Biden was reflexively spouting before the Russian Tanks had even had a chance to top off their fuel tanks after crossing the Ukraine border