US President Barack Obama has doubled an initial 500 million US dollar (£410 million) commitment to a fund which helps developing nations fight climate change and adapt to its consequences.
The announcement came as he had just three days left in office.
The incoming Trump administration and some Republicans oppose the programme.
The State Department's announcement on Tuesday brings US contributions to the Green Climate Fund to 1 billion US dollars (£820 million) since 2016. The fund helps poor countries reduce carbon emissions by promoting clean energy and spurring private investment in the field.
"This administration has committed to this fund, in fact helped stand it up, establish it," said State Department spokesman John Kirby.
"And it is entirely in keeping with the work that we've been doing across the interagency to try to look for ways to stem the effects of climate change, and this fund helps other economies, other countries develop their own initiatives and help them deal with this."
Mr Obama promised a total of 3 billion US dollars (£2.46 billion) to the fund in 2014 as part of the Paris climate change accord, but it is far from certain that the full amount will be pledged.
President-elect Donald Trump and a number of Republican politicians have complained that support for the fund was not specifically approved by Congress.
The administration argues that the current fiscal year's budget allows it to take the money from an unobligated portion of a total of 4.3 billion US dollars (£3.5 billion) in economic support fund assistance. The previous 500 million US dollar (£410 million) instalment was made in the same way.