Washington: Democrats in Pennsylvania as set to choose between Hillary Clinton and Barak Obama on Tuesday as both candidates push for the party’s presidential nomination.

Clinton is favoured to win but she needs a convincing victory to recover ground on Obama.

Her one-time 20-point lead has slipped to single digits in many polls amid an onslaught of advertisements by Obama, who has heavily outspent her in the state.

In the run-up to the poll, Clinton released an ad featuring images of Al Qaida leader Osama bin Laden and touting her strength.

Obama's camp meanwhile accused her of using "the politics of fear."

The Pennsylvania vote marks the final stages of the Democratic nomination. Nine more contests are scheduled before the campaign concludes in early June.