Bill Clinton has taken issue with President Barack Obama's Syria policy saying "it's a bad mistake" for the United States not to intervene, US media reported Thursday.

Speaking at a private event, the Democratic party icon and former president made a rare foray into foreign policy at a moment when the Obama administration is under growing pressure to act on Syria and arm the rebels.

He warned Obama -- with whom he has a close working relationship -- that failure to act risks leaving him looking "lame" and like "a wuss."

"Some people say, 'See what a mess it is. Stay out.' I think that's a bad mistake. I agree with you about this," he told Senator John McCain, according to the online Politico website, which first reported the comments.

"Sometimes it's just best to get caught trying, as long as you don't overcommit," he added.

At the event hosted by the McCain Institute which was closed to the media, Clinton compared Obama's dilemma over Syria to the 1999 Kosovo crisis in which he helped organize NATO's intervention.

Any president had to look at the wider picture to safeguard national security and save lives, Clinton said, even if there is little public appetite for any intervention.

"You just think how lame you'd be," he said, according to the Daily Beast, which also obtained an audio of the event.

"Suppose I had let a million people, two million people be refugees out of Kosovo, a couple hundred thousand people die, and they say, 'You could have stopped this by dropping a few bombs. Why didn't you do it?' And I say, 'because the House of Representatives voted 75 percent against it?'

"You look like a total wuss, and you would be."

Clinton did not appear to have made any reference though to the 1994 Rwanda genocide in which 800,000 people, mainly Tutsis, were killed in just 30 days.

The Clinton administration did not intervene in the massacres, something which Clinton now calls his "biggest regret."

Referring to Clinton's comments on Syria, State Department spokeswoman Jen Psaki said: "As President Clinton knows, these decisions are very difficult, and they require careful weighing of the facts."

Obama's "focus, as we've talked about quite a bit in here over the last couple of days, is on making the best decision that will help bring an end to the suffering of the Syrian people, while balancing with our own national security interests and those of the region."

But she said no decision had yet been taken on whether to arm the Syrian rebels, while acknowledging that the situation on the ground was worsening.