Chief executives of some of the largest companies in the US have urged President George W Bush to introduce measures to tackle global warming. The executives from nine corporations said Mr Bush should support a mandatory cap on greenhouse gas emissions.

Mr Bush will address the issue in his State of the Union speech on Tuesday, but will not introduce binding rules for emissions, the White House says.

President Bush has in the past rejected mandatory controls on greenhouse gases. The US withdrew from the Kyoto protocol in 2001.