New UK Prime Minister Rishi Sunak faced condemnation after his spokesman announced Thursday he will not attend next month's COP27 UN climate summit in Egypt due to "pressing domestic commitments".

Britain hosted the last such summit, COP26, when it stressed the importance of global leaders convening to discuss climate change amid growing criticism of their failure to meet vital carbon reduction targets.

Sunak's decision came on the same day the United Nations warned that countries' climate pledges leave the world on track to heat by a potentially calamitous 2.6 degrees Celsius (36.7 degrees Fahrenheit) this century.

It also follows his moves to stop allowing the government's COP26 minister Alok Sharma and climate minister Graham Stuart attending cabinet, as they had done under his predecessors.

Sunak was only installed Tuesday as the UK's third leader in two months.

He replaced predecessor Liz Truss after she was ousted just seven weeks into her tenure over a disastrous tax-slashing mini-budget unveiled last month that sparked economic turmoil.

Truss had been set to attend the UN climate conference in Egypt's Sharm El-Sheikh, British media said.

"The prime minister is not expected to attend COP27 and this is due to other pressing domestic commitments including preparations for the Autumn Budget," his spokesman told reporters, referring to a November 17 announcement of the government's revised fiscal plans.

Downing Street insisted Sunak was "absolutely committed" to supporting COP27, denying he was downgrading the importance of tackling the climate crisis.

But he faced immediate criticism from opposition politicians and environmental groups.

"This is a massive failure of climate leadership," said Ed Miliband, the main opposition Labour party's former leader and now climate change spokesman.

"We were the COP26 hosts and now the UK prime minister isn't even bothering to turn up."

He accused Sunak of failing to understand "that tackling the climate crisis isn't just about our reputation and standing abroad, but the opportunities for lower bills, jobs, and energy security it can deliver at home".

Rebecca Newsom, head of politics at Greenpeace UK, compared Sunak's decision to "a runner failing to turn up with the baton at a crucial stage of the relay".

"Coming just after the ousting of Alok Sharma from the cabinet, this suggests that the new prime minister neither takes the climate crisis seriously enough, nor recognises the opportunities for Britain to take a leadership role in helping to solve it."