U.S. President Barack Obama, defending his foreign policy record at a time of anti-American rage in the Muslim world, fired back at suggestions from Republican Mitt Romney that the president has been weak with allies and enemies alike.

According to The Associated Press, in an interview airing the night before Obama meets with other world leaders at the United Nations, the president said, "If Gov. Romney is suggesting that we should start another war, he should say so."

It was Obama's most direct rebuttal yet to persistent skepticism by his White House rival on his handling of an unraveling situation in the Middle East. Romney has charged the U.S. stance has been marred by miscalculations, mixed messages and appeasement.

The foreign policy arguments come as both candidates sharpen their strategy just six weeks ahead of Election Day. Speaking to reporters on a flight to Colorado Sunday, Sept 23 night, Romney acknowledged he was slipping behind Obama in several swing states and said he would spend more time with voters in the coming weeks.

"I think the fundraising season is probably a little quieter going forward," he said following a weekend largely devoted to raising money in California.

Obama is launching a new campaign offensive Monday with his first television advertisement targeting Romney's comments about Americans who don't pay income taxes. The ad, which was to start running in swing state Ohio, argues that Romney should stop attacking others on taxes and "come clean" on his own.

The ad uses Romney's comments to wealthy donors that 47 percent of Americans don't pay income taxes, believe they are victims and feel entitled to government assistance. It shows Romney saying, "My job is not to worry about those people."

The 30-second spot signals that Obama will keep making the wealthy Romney's taxes a campaign issue even after the Republican released a second year of information about his personal finances last week.