Barges carrying masses of coal float down the in Samarinda in Indonesia, one of the world's biggest exporters of coal

The world's biggest banks are ploughing hundreds of billions of dollars into coal mining despite claiming to be leaders in the fight against climate change, according to a report issued at a UN conference Wednesday.

Many of the world's biggest banks have started to cut back on their financing of coal, the burning of which leads to greenhouse that cause , and are proclaiming themselves climate leaders.

But they have provided more than $257 billion (243 billion euros) in coal financing over the past six years, compared with just $105 billion for all renewable energies, according to the study by a coalition of environment groups including Friends of the Earth.

"The largest and most powerful financial institutions on both sides of the Atlantic have continued to provide billions of dollars to companies working to entrench global dependance on carbon-intensive ," the report said.

Scientists say the world's energy sources must shift quickly away from coal and other fossil fuels to renewables if global warming is to be kept below 2 degrees Celsius (3.6 Fahrenheit) from pre-Industrial Revolution levels.

At the UN conference, negotiators are trying to seal an historic accord to come into effect from 2020 that would keep global warming to the 2-degree-C threshold and save mankind from catastrophes caused by rising temperatures.

"The window for holding below the critical two-degree threshold is rapidly closing," the report said.

"Genuine leadership from the financial sector must begin with cutting off financing for high-carbon energy sources, starting with and power plants that will lock in our carbon emissions for years to come."