Image caption President Obama originally vowed to pursue stronger smog regulations

US President Barack Obama has scrapped proposals to tighten rules on air pollution.

He ordered the Environmental Protection Agency (EPA) to shelve plans to reduce concentrations of ozone - one of the main contributors to smog.

Mr Obama said he was pulling the measure as part of a government effort to reduce regulatory burdens and uncertainty as the economy struggles.

Business groups and Republican politicians welcomed the decision.

But environmentalists condemned the move.

The BBC's Marcus George in Washington says that, coming after new figures showing zero employment growth over the last month, the measure underscored just how sensitive the president has become about America's decimated economy.

'Decision on merits'

Mr Obama asked EPA administrator Lisa Jackson to withdraw the draft rules, saying in a statement on Friday: "I have continued to underscore the importance of reducing regulatory burdens and regulatory uncertainty, particularly as our economy continues to recover."

This is a new low for President Obama Kieran Suckling, Center for Biological Diversity

The EPA estimated a new smog standard would cost up to $90bn (£55bn) a year - opponents said it would cost more.

The rules could also have saved as much as $100bn in health costs, and helped prevent as many as 12,000 premature deaths from heart and lung complications, according to the EPA.

Ozone is a lung irritant, connected with asthma and other respiratory conditions.

The administration defended its decision to reporters on Friday as a decision on the merits, not the result of industry pressure.

House Speaker John Boehner's office praised Mr Obama's decision as a boost to business growth, but added that the single proposed regulation had been "the tip of the iceberg".

The move angered environmentalists.

"This is a new low for President Obama," said Kieran Suckling, executive director of the Center for Biological Diversity.

Gene Karpinski, the president of the League of Conservation Voters, said: "The Obama administration is caving to big polluters at the expense of protecting the air we breathe.

"This is a huge win for corporate polluters and a huge loss for public health."

The White House said a new standard would be issued in 2013, after the science behind the levels has been updated.

But our correspondent says campaigners are already talking of a legal challenge that could force the administration to reconsider.