President Barack Obama has named two political veterans to head an independent US commission investigating the Gulf of Mexico oil spill, amid criticism of the government's response.

They are ex-Democratic Senator Bob Graham and former Republican environment chief William Reilly.

The president said he wanted to make sure such a disaster never happened again.

The panel has six months to compile its report.

President Obama's administration has been forced to defend its record in dealing with the spill.

'Hold Washington accountable'

The oil leak began more than a month ago, when a rig leased by BP exploded, killing 11 people and spewing millions of gallons of oil into the ocean.

The spill has reached Louisiana and is threatening Florida and Cuba.

So far, BP has borne the brunt of public outrage over the spill, but analysts say there is now also a growing sense of anger towards the government.

In his weekly radio and internet address, Mr Obama stressed that no government employee or elected official would serve on the seven-member panel. The remaining five members have not yet been named.

Mr Reilly led the Environmental Protection Agency under President George Bush Sr, while Mr Graham served in the senate from 1987-2005.

"The purpose of this commission is to consider both the root causes of the disaster and offer options on what safety and environmental precautions we need to take to prevent a similar disaster from happening again," the president said.

He said that the government was doing all it could to help struggling fishermen and other businesses and communities affected by the spill.

But he said the panel would also investigate whether more could have been done to prevent the disaster.

"Even as we continue to hold BP accountable, we also need to hold Washington accountable."

Mr Obama also dismissed calls to halt his programme of expanding offshore oil drilling in the wake of the spill.

"The Gulf of Mexico can play an important part in securing our energy future," he said, before adding:

"We can only pursue offshore oil drilling if we have assurances that a disaster like the BP oil spill will not happen again."