U.S. President Barack Obama said in the second presidential debate on Tuesday that he is "ultimately responsible" for what happened in the attacks on the American consulate in Benghazi, Libya last month.

"I'm the president and I'm always responsible," Obama said in the high-stake debate with his Republican rival Mitt Romney.

The attacks on the U.S. consulate in Benghazi on the night of Sept. 11, which resulted in the deaths of U.S. Ambassador to Libya Christopher Stevens and three of his staff, shocked the United States.

U.S. Secretary of State Hillary Clinton said on Monday that she took responsibility for the deadly assault on the American consulate in Benghazi, in an apparent bid to take the heat off Obama.

The Obama administration has been under fire from the Republicans who accused it of being unprepared for the attacks and trying to cover up its mishandling of the issue in the wake of the assault.

The aggressive Obama assailed Romney for exploiting the consulate attacks to score political points.

"The suggestion that anybody on my team, whether it's a secretary of state, our UN ambassador, anybody on my team, would play politics or mislead when we've lost four of our own, governor, is offensive," he said.

Romney fought back hard on the issue, accusing Obama of continuing to go to a fund-raising tour the day after the attacks and saying that the deadly assault represents the "unraveling" of Obama's Middle East policy.

"There was no demonstration involved. It was a terrorist attack and it took a long time for that to be told to the American people," he said.

"This calls into question the president's whole policy in the Middle East," Romney said, calling the strategy "unraveling before our very eyes."