A key U.S. congressional panel has approved a landmark bill aimed at combating climate change, days after Democratic lawmakers reached a compromise on the measure.

The House Energy and Commerce Committee approved the bill Thursday by a 33-25 vote, split largely along party lines, with Democrats supporting and Republicans opposing.

A key part of the bill calls for a so-called cap-and-trade system that would allow businesses to buy permits to emit greenhouse gasses from other firms that use less energy.  

The bill also calls for a 17 percent cut of heat-trapping greenhouse gas emissions below 2005 levels by 2020.  Committee chairman Henry Waxman and others initially called for a 20 percent cut, but agreed to a lower level after objections from Democrats who represent states heavily dependent on coal-power plants and other heavy industries.

The measure also requires utilities to generate 15 percent of their electricity supplies from renewable energy sources by 2020.  

Waxman and other supporters hail the bill as the first of its kind to seriously address climate change.  But it faces likely changes in other House committees, and its passage in the Senate is not assured.

Some information for this report was provided by AP and Reuters.