American leaders say the US is getting on with the job of cutting emissions and may still achieve its reduction target despite President Donald Trump.
But environmental groups warn the official US delegation at the UN climate negotiations is blocking any reference to finance to help developing countries meet their targets and is "infecting the positive spirit" of other nations.
The COP23 talks are the first global meeting on climate since Mr Trump announced in June he would pull the US out of the Paris agreement unless it was made more favourable to America.
An unofficial coalition of American senators, state governors, mayors, business leaders and environmental groups has set up shop next to the conference venue in Bonn, highlighting the action they are taking to reduce emissions.
Billionaire businessman Michael Bloomberg says the country is already halfway to meeting its Paris target "with virtually no help from the federal government".
"The American government may have pulled out of the Paris agreement, but the American people are committed to its goals and there is nothing Washington can do to stop us," he said in Bonn on Saturday.
The coalition of states, cities and business that has signed up to the "we are still in" pledge on climate action accounts for half the US economy.
Fijian Prime Minister Frank Bainimarama, who holds the COP23 presidency, said it is a fantastic show of how progress could be made through the leadership of non-state actors.
Mr Bloomberg wants the unofficial American pledge to be accepted alongside the promises every other country has made.
"We will continue measuring and reporting our progress on reducing emissions, just as every other nation has committed to do, so the world can hold the United States accountable for reaching our commitment," he said, applauding efforts from Fiji to open up the negotiations to non-state actors.
However, at a reporting session on negotiation progress later on Saturday, Morocco's representative said while countries appreciated the need to encourage action by non-state actors, they had not reached any agreement on whether, or how, to include them in talks.
Meanwhile, in official negotiations, environment group Action Aid - part of the Climate Action network - says the Americans are not playing things as low key as hoped.
"This week we have seen the US as active as it used to be, as obstructive as it used to be," Action Aid's Harjeet Singh told reporters.
Its negotiators were actively blocking all references to finance, and other parties including Australia, Canada and the European Union were starting to follow.
"We thought that after facing a season of devastating hurricanes in the US, the government would be far more empathetic to the people and countries who are being battered by climate impacts, but we were wrong," Mr Singh said.
"The US is not just blocking, it's also pulling others down ... the US actions are infecting that positive spirit."
