New fuel efficiency rules for cars and light trucks were finalized by US regulators on Thursday, raising fuel economy standards and for the first time regulating greenhouse-gas emissions blamed for global warming.

The announcement is part of a broader pledge by President Barack Obama to shift the US economy towards cleaner forms of energy and curb climate change, though efforts to achieve comprehensive reforms have so far floundered in Congress.

It is a "historic" standard that would be a "win-win program for our economy and our environment", said Lisa Jackson, head of the Environmental Protection Agency (EPA).

Obama first directed his administration to raise fuel economy standards in May 2009 in an effort to curb pollution from vehicles, which account for about one quarter of all climate-damaging emissions from the US.

Environmentalists and carmakers welcomed the new rules. They had agreed to back the higher fuel economy requirements after talks with the Obama administration last year.

"While these requirements are very challenging, we feel confident that GM will be able to achieve the mandated fleet fuel economy targets," General Motors Co in a statement said.

It was separately announced by GM that the first Chevy Volt had rolled off the factory production line. The plug-in hybrid, which enters mass production later this year, is a central element of GM's strategy to green its car fleet.

The Volt is powered by an electric motor with a range of about 64 km, after which a petrol motor kicks in that extends its range by nearly 500 km. (With Inputs from Agencies)