None of the US nine leading insurers have taken action to stop underwriting or investing in the coal industry, undermining their European peers in the process.
This poses a significant risk to health and the environment, a new report from the Unfriend Coal campaign warns, with AIG, Chubb and Liberty Mutual coming in for particular scrutiny.
In contrast, Europe's four largest primary insurers have all restricted coverage for coal, with Allianz, Generali and AXA tightening their policies this year after Zurich did the same in 2017.
At least 19 insurers with more than $6trn (£4.7trn) in assets have divested from the industry, up from $4trn last year, with Swiss Re ranked highest for action on coal and climate change.
"US insurers are betraying their shareholders, their customers and the wider public by continuing to support fossil fuels," Greenpeace USA executive director, Annie Leonard, said.
"They should follow the lead of their European peers who realise coal is a bad investment, causes thousands of premature deaths, and must be phased out to avoid dangerous climate change."
The UN believes at least 59% of all coal power must be phased out by 2030 to meet the Paris Agreement's aim of restricting global warming to 1.5°C above pre-industrial levels.
After assessing 24 of the world's largest insurers, the Unfriend Coal campaign ranked Swiss Re, Generali, Zurich, Allianz and AXA among the top five for action on coal and climate change.
US insurers Liberty Mutual, Berkshire Hathaway, W.R. Berkley, AXIS Capital and MetLife complete the bottom five, while Asia-Pacific insurers also continue to insure and invest in coal.
However, it was found that the policies of some European insurers contain large loopholes, only restricting coverage for certain projects, and limiting their divestment.
Willis Towers Watson said that finding alternative sources of coal insurance would likely become increasingly challenging if US insurers follow the European lead.
While the Unfriend Coal campaign report added: "Just as significant as the contraction in insurance market capacity may be the withdrawal of expertise."
