The New York senator said the ads were partly responsible for Obama's rising popularity in Pennsylvania where figures indicate he has narrowed the margin to a few percentage points with the April 22 primary approaching.

Obama aides credit the Illinois senator's recent bus tour across the state for his rising figures, the Chicago Tribune said.

One Obama ad claims he is has not taken oil company money. The newspaper said Obama and Clinton have accepted donations from oil company executives.

Obama was back in Pennsylvania this week and also was pouring millions of dollars into television ads that inspired a furious Clinton response. Clinton communications director Howard Wolfson said Obama has spent $6.5 million on TV ads in Pennsylvania, while the Clinton campaign has spent $2.5 million.

Clinton was in the western part of the state with military veterans while Obama was in eastern Pennsylvania, visiting high schools in Malvern and Levittown.