The United States in December designated a key Syrian rebel group, the al-Nusra Front, as a terrorist entity.

U.S. officials argued it was a necessary step that would not weaken the ability of other rebels to combat the Syrian military.

Appearing before the Senate Armed Services Committee on Thursday, Panetta and Dempsey were asked by Arizona Sen. John McCain, the leading Republican proponent of a more aggressive backing of Syrian rebels, whether they supported the idea of arming them.

"We do," answered Panetta.

"We did," answered Dempsey.

They did not get a chance to explain as McCain moved on to another topic.

But McCain used the brief answers to urge President Barack Obama to consider the plan, saying in a statement that "the time to act is long overdue, but it is not too late."

"The crisis in Syria represents a graphic failure of American leadership. I urge the president to heed the advice of his former and current national security leaders and immediately take the necessary steps, along with our friends and allies, that could hasten the end of the conflict in Syria," McCain said in the statement.

Obama spoke last month about hesitation to get more involved in the civil war in Syria.

"Syria is a classic example of where our involvement, we want to make sure that not only does it enhance U.S. security, but also that it is doing right by the people of Syria and neighbors like Israel that are going to be profoundly affected by it. And -- and so it's true sometimes that we don't just shoot from the hip," he told CBS News.