Washington - Less than one week before the US general election, Republican vice presidential candidate Sarah Palin took centre stage in the campaign Wednesday with a major policy speech on energy, while Democratic rival Barack Obama launched his first television ad directed against Palin.

Palin, running alongside John McCain, promised an "all-of-the- above approach" to end US dependence on foreign energy and encourage the production of domestic sources, focussing on renewables as well as more oil drilling. She slammed Obama for a "long, laboured agenda of inaction" on energy.

McCain has touted Palin, governor of oil and natural-gas rich Alaska since 2006, as a key advisor for energy policy should he make it into the White House.

The Obama campaign meanwhile launched their first direct attack on Palin's suitability for the vice presidency, questioning McCain's judgement in picking someone with little economic experience.

The television ad highlights past McCain comments that economics "is not something I've understood as well as I should" and suggesting he would rely on a running mate's expertise on the issue.

"His choice?" asks the ad, before showing a video of Palin winking at the camera in her debate with Obama's running mate Joe Biden.

Palin has been a flashpoint of the election ever since she was chosen by McCain in August. She has energized the Republican base for her conservative social views and image as a reformer in Alaska. Left-leaning commentators have derided her as not experienced enough to back McCain, who at 72 would be the oldest president ever to begin a first term.

Obama's campaign has been careful about directly criticizing McCain's choice of Palin in the past, focussing instead on the top of the ticket and leaving the attacks on his running mate to surrogates. (dpa)