The Kremlin said on Sunday contacts with U.S. President Donald Trump's team were moving ahead very well but that it was too early to expect instant results due to the level of damage done to relations under Trump's predecessor Joe Biden.

Separately in Belgium, nations supporting Ukraine pledged billions more in military aid and raised doubts about Moscow’s desire for peace.

The U.S. ambassador to Ukraine is stepping down from her post after nearly three years in Kyiv. The departure of Bridget Brinks comes at a time of uncertainty over the Trump administration's attempts to broker a peace deal to end the Russia-Ukraine war.