The American Lung Association (ALA) has issued a report in the US calling for more radical action to combat the problem of emissions.

According to the ALA around half of the population continues to breathe unhealthy air.

John Kirkwood, president and chief executive officer of the ALA, one of the nation's oldest and largest public health advocacy groups, claimed: 'Americans' right to breathe clean air is being threatened.'

The report, which has analysed data since the mid-1990s, suggested 137 million Americans are subjected to unhealthy amounts of smog.

However, Environmental Protection Agency (EPA) Administrator Christie Whitman said adequate measures were already being taken.

'We share the same goal as the American Lung Association,' Ms Whitman said. 'We believe that the President's Clear Skies initiative, along with other EPA programs already underway, will achieve the results we all are looking for - and sooner than under current law.'

The ALA is now calling for cleaner fuel standards, and stricter pollution control requirements for motor vehicles, and for power plants.