WASHINGTON -- Brazil pledged Tuesday to restore millions of acres of forests and expand renewable energy use, as the United States and Brazil worked to build momentum toward a budding global climate treaty.

Rich and poor countries alike have been putting forth their commitments, known as nationally determined contributions, to reduce emissions as part of the treaty, which world leaders hope to finalize later this year in Paris. Although Brazil has yet to announce how much it will pledge to cut emissions, the South American nation began unveiling elements of its offer during a visit by Brazilian President Dilma Rousseff to the White House.

As part of its plan, Brazil is vowing by 2030 to restore and reforest 12 million hectares. Brazil also plans to expand renewable energy sources other than hydropower to between 28 per cent and 33 per cent of its total energy mix by 2030.

And in the electricity sector, the U.S. and Brazil jointly announced intentions to increase their share of renewable, non-hydropower sources to 20 per cent by 2030. Brian Deese, President Barack Obama's senior adviser, said boosting renewables that high in the U.S. would be dependent on controversial power plant emission limits that the Obama administration has proposed.

"We believe that this is an ambitious target, but one that is actually achievable and will create new low-cost opportunities for the American economy," Deese said. "To achieve it, we're going to have to continue to hit our marks in implementing the regulations we've identified to date."

The U.S. has already announced its full commitment to the climate treaty: a reduction of greenhouse gas emissions of up to 28 per cent by 2025, compared to 2005 levels. But a key sticking point in the climate treaty has been whether developing nations like Brazil will be willing to make substantial contributions. Poorer nations have balked, arguing that industrialized nations that have polluted more historically bear more of the responsibility for curbing climate change.

The announcement comes on the second day of Rousseff's visit to Washington, where she met with Obama in the Oval Office on Tuesday morning.

In their visit, Obama and Rousseff have been working to show they've moved beyond tensions sparked by the revelation nearly two years ago that the U.S. was spying on Rousseff. She cancelled a planned state visit in response. Officials in both countries say neither leader is interested in rehashing the spying issues this week and instead want to focus on ways to deepen co-operation.