State Street Corp's asset management arm launched its first fossil-fuel free exchange-traded fund, citing investors' concerns over climate change.

The ETF is among the first of its kind offered in the United States, as climate activists encourage mainstream investors to steer clear of oil, gas and coal stocks.

State Street Global Advisors, which launched the fund, is the No. 3 U.S. ETF provider with about $419 billion in assets under management, according to Morningstar Inc.

"Motivated by concerns surrounding climate change, a growing number of our clients are seeking solutions that can help them divest from fossil fuel reserves while maintaining their strategic asset allocations," said James Ross, who heads State Street's SPDR ETF business.

The SPDR S&P 500 Fossil Fuel Free ETF will hold stocks in Standard & Poor's 500 companies that are not involved in coal, oil or gas. The ETF was developed with the Natural Resources Defense Council, which State Street described as a "cornerstone investor" in the fund.

Investors are focusing on climate risk as world leaders gather in Paris to hash out an agreement to rein in global warming.

Environmental activist group 350.org and NGO Divest-Invest said on the sidelines of the talks on Wednesday that more than 500 institutions around the world holding $3.4 trillion in assets have made commitments to divest fossil fuels, from 181 institutions representing $50 billion in 2014.

Climate funds are a relatively new tool for environmentally minded investors, and remain a tiny part of the $30 trillion-plus mutual fund universe.

U.S. investment company Etho Capital launched an ETF similar to State Street's earlier this year, the Etho Climate Leadership exchange-traded fund. The ETF tracks the performance of some 400 U.S. companies outside the fossil fuels industry.

Dozens of other climate-focused mutual funds are available to investors in Europe and Asia, though several of the biggest have stakes in traditional oil and gas companies, according to Reuters data.