London: Prime Minister Liz Truss will join King Charles III at memorial services around Britain for Queen Elizabeth, Downing Street has said, while denying she would officially accompany him after the idea drew criticism.

Media commentators and social media users had whether there was a political motivation for Truss joining the king to lead mourning in Scotland, Northern Ireland and Wales.

But the prime minister's office was at pains to play down any controversy, with Truss still in the first week of her premiership after having been appointed by the queen on Tuesday.

"The PM is not 'accompanying' the king and it is not a 'tour'. She is merely attending these services," Downing Street said.

A day earlier, Downing Street had said that Truss "will join the king as he leads the national mourning across the United Kingdom, attending services of reflection" in Scotland, Northern Ireland and Wales.

"It's not a requirement. But the prime minister believes it's important to be present for what will be a significant moment of national mourning around the United Kingdom."

The initial announcement had drawn criticism.

"Out of genuine interest... why?" tweeted Alastair Campbell, the former media chief for ex-prime minister Tony Blair, in response to a BBC report that Truss would accompany Charles.

"I can see how this helps Liz Truss. I cannot see how it helps King Charles," added Financial Times writer Henry Mance, adding that the "well-wishing atmosphere seen outside the palace yesterday will be hard to recreate if a politician is present and meddling".

Charles is visiting all the component nations of the United Kingdom in an operation codenamed "Spring Tide" following the death of Britain's longest serving monarch.

Buckingham Palace on Saturday announced fuller plans for Charles' itinerary leading up to the queen's state funeral in London on September 19.

The king is first due to attend a service of "prayer and reflection" for the queen at St Giles’ Cathedral in the Scottish capital Edinburgh on Monday.

Charles will then fly to Belfast on Tuesday for a similar service at St Anne's Cathedral in Belfast, Northern Ireland, and will travel to Wales on Friday.

Details for the Welsh trip have yet to be released.