However, in an effort to raise the US profile in Madrid, House speaker Nancy Pelosi will led a 15-member congressional delegation to "reaffirm the commitment of the American people to combating the climate crisis."

The US, at Trump's direction, is withdrawing from the Paris climate accord, which set a goal of limiting global temperature rises to well within two degrees Celsius (3.6 Fahrenheit) from pre-industrial levels.

Spain stepped in to host the COP25 meeting, which seeks to boost commitments to fight climate change, after Chile pulled out due to civil unrest.

"The United States will continue to participate in ongoing climate change negotiations and meetings -- such as COP25 -- to ensure a level playing field that protects US interests," the US State Department said Saturday.

The US team will be headed by ambassador Marcia Bernicat, principal deputy assistant secretary of state for oceans and international environmental and scientific affairs.

Pelosi, calling climate change "the existential threat of our time," announced a delegation of Democrats drawn from both the House and the Senate, with no members of Trump's Republican party.

The president has cast the Paris climate accord as elitist and unfair to the US, saying when announcing his decision to withdraw that he was "elected to represent the citizens of Pittsburgh, not Paris."

But scientists say the accord is vital to check the worst damage from global warming, such as increasing droughts, rising floods and intensifying storms.

The United States is the world's second biggest emitter of greenhouse gases after China, and is the only country to pull out of the Paris agreement.

The final US withdrawal from the landmark accord is scheduled for November 4, 2020, a day after the next presidential election.

Several Democratic presidential aspirants have said that, if elected, they would immediately return to the agreement.