A senior South African diplomat says his country cannot rule out boycotting the COP26 summit in Glasgow next month.
Clayson Monyela, South Africa's head of public diplomacy, told Sky News the current rules for delegates from COVID red list countries means the conference could "collapse".
He added that nations on the UK's red list have essentially been "banned" from attending the summit due to rules which mean a vaccinated delegate would have to quarantine for five days, while an unvaccinated delegate would have to isolate for 10.
He added South Africa is now considering whether or not to send delegates and negotiators to the conference.
Mr Monyela added other red list countries in Africa and South America "are asking themselves similar questions".
The UK is set to host the United Nations Climate Change Conference, referred to as COP26, between 31 October and 12 November. More than 30,000 people from roughly 200 countries are expected to attend, but some associated events will happen online.
Mr Monyela said: "A decision on whether South Africa will choose not to attend has not been made yet, but we can't rule it out.
"But it is unreasonable for South Africa to be on the UK red list, there is no scientific evidence to support this. It makes no sense."
Mr Monyela added: "I can't speak for other countries, but I know the questions South Africa is asking, many of the countries on the continent and in South America are asking similar questions.
"I think that's the issue that the United Nations and the UK need to think about. At the rate things are going, you risk having a 'European COP26' to the exclusion of Africa and South America.
"How is that then the United Nations conference on climate change? When you have basically banned other countries from participating?"
Mr Monyela also highlighted how "decisions are taken on a consensus basis" at the conference and it therefore presents a very serious issue if other countries choose not attend.
He added that South Africa has been "playing a leading role on climate change" and "excluding" them and other countries through quarantine rules could lead to the "collapse of the conference" altogether.
The government's COP26 president Alok Sharma said in a statement: "We are working tirelessly with all our partners, including the Scottish Government and the UN, to ensure an inclusive, accessible and safe summit in Glasgow with a comprehensive set of COVID mitigation measures.
"This includes an offer from the UK government to fund the required quarantine hotel stays for registered delegates arriving from red list areas and to vaccinate accredited delegates who would be unable otherwise to get vaccinated.
"Ensuring that the voices of those most affected by climate change are heard is a priority for the COP26 Presidency, and if we are to deliver for our planet, we need all countries and civil society to bring their ideas and ambition to Glasgow."
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