LONDON, March 9, 2025 (BSS/AFP) - Britain's King Charles III made an appeal on Saturday for unity in "uncertain times", as the 76-year-old monarch emerges as a key figure in the UK's diplomatic drive over Ukraine.

Britain and European countries have been scrambling to present a united front following US President Donald Trump's sudden withdrawal of support for Ukraine three years into Russia's invasion.

By tradition, the UK head of state's role is politically neutral. But in recent days, Charles has hosted Ukrainian President Volodymyr Zelensky at his private estate and invited Trump for an historic second state visit.

On Monday, Charles will deliver a message for Commonwealth Day, which celebrates the 56-nation club of mostly former British colonies.

According to extracts published late on Saturday, Charles -- who heads the Commonwealth -- said nations' differences should be a "source of strength".

"In these uncertain times, where it is all too easy to believe that our differences are problems instead of a source of strength and an opportunity for learning, the Commonwealth's remarkable collection of nations and peoples come together in the spirit of support and, crucially, friendship."

Earlier on Saturday, British leader Keir Starmer said that Australia's Prime Minister Anthony Albanese was considering joining a group of countries prepared to protect an eventual ceasefire in the Russia-Ukraine war.

British officials have held talks with around 20 countries interested in being part of the so-called "coalition of the willing," a UK official said on Thursday.

The official refused to name the nations but said they were "largely European and Commonwealth partners".

Charles' message is set to be published in full on Monday.