Queen Elizabeth II, the ceremonial head of state of the United Kingdom and of 15 other members of the Commonwealth, will not attend the United Nations' COP26 climate summit.

The hereditary monarch, who has spoken out recently about climate change and who had initially been expected to host part of the gathering, said through her office she "regretfully" would not now be able to attend in person.

Buckingham Palace said the 95-year-old will, however, deliver her speech as a recorded message.

The BBC noted she had recently spent time in hospital and that her doctors had advised her to rest as much as possible.

While she was never going to be among the elected lawmakers and world leaders taking part in the main sections of the summit, and while she has no decision-making powers, the BBC reported that the queen was slated to deliver a speech at a reception during the event, which will run from Oct 31 to Nov 12 in Glasgow, Scotland.

Buckingham Palace said in a statement: "Following advice to rest, the queen has been undertaking light duties at Windsor Castle. Her majesty has regretfully decided that she will no longer travel to Glasgow to attend the evening reception of COP26 on Mon, Nov 1."

The statement said the queen was "disappointed" she could not attend. She is expected to follow the delegates' progress remotely.

The palace said she had "reluctantly accepted medical advice to rest for the next few days".

Peter Westmacott, a former UK ambassador to the United States, said on Radio 4's Today program the queen's non-attendance will be a "blow" for organizers, but is unlikely to impact the summit's outcome.

He said her attendance would have been the "icing on the cake" but noted Prince Charles and several other members of the royal family are still expected to attend.

The queen, who spent a night in hospital last week for medical checks, has also recently canceled an official visit to Northern Ireland on health grounds.

The monarch was widely reported earlier this month as having said she finds it annoying when people in power talk about the challenge of climate change but fail to take action.

The Guardian newspaper quoted her at the time as having been overheard saying: "It's really irritating when they talk, but they don't do."

The Daily Express newspaper said some observers now fear a "domino effect", with other world leaders using the queen's absence as a reason not to attend the summit.