US venture capital firm Kleiner Perkins Caulfield & Byers (KPCB) is reportedly attempting to raise more than $400m (£200m) for a new "Green Growth" fund designed to invest in later-stage clean tech firms with established technologies.

According to reports at private equity news site peHUB, the firm is in the process of pitching the fund to investors. It claims the completed fund is expected to raise more than $400m for investing in mature clean tech firms, select public investments, carve outs and spinouts.

Kleiner has built a strong reputation as a clean tech backer, most recently through investments in US recycling specialist RecycleBank and the US arm of Norwegian electric car firm Think. Last year, the company also appointed Al Gore as a partner in its clean tech division. Gore is now reported to be involved in the pitching of the new fund.

The new "Green Growth" fund is expected to run parallel to Kleiner's existing $200m green fund, which is focused on earlier-stage clean tech firms.

Writing at the VentureBeat blog, Matt Marshall said the new fund highlighted the rapid maturing of clean tech investments. "Many environment-related projects, including solar thermal, electric cars and bio-fuel manufacturing, require huge amounts of capital," he wrote. "Kleiner had earlier raised $200m to invest in early-stage green companies, but it does not have enough money to invest large chunks of cash in more mature companies as they move to the manufacturing stage."