Climate negotiators have kicked off 11 days of talks in Germany amid uncertainties about whether the United States will remain committed to the landmark Paris climate agreement.
The May 8-18 gathering in Bonn is meant to start drafting a guide for countries to implement the 2015 climate deal, which calls for limiting global warming by curbing fossil fuel emissions.
Nearly 200 countries have signed the accord, but there has been speculation that U.S. President Donald Trump may withdraw the world's No. 2 carbon emitter.
There have also been suggestions that the United States might stay in if it is allowed to reduce the commitments made under Trump's predecessor, Barack Obama.
Meanwhile, the White House said it had postponed a planned May 9 meeting to discuss whether the United States should withdraw from the Paris deal.
This is the second time a meeting of top aides on the issue has been delayed.