"I think we should have been more willing to confront Assad"
The former presidential campaign rival of Donald Trump called for Syrian airstrikes, just hours before Mr Trump ordered them.
President Trump launched 59 cruise missiles on an airfield in Syria just days after at least 80 people were killed in a chemical attack on Idlib province.
But even before it happened, Hillary Clinton suggested doing just that.
During the 2016 campaign, Mrs Clinton expressed her support for a no-fly zone over Syria and more direct support for protesters.
In a wide-ranging interview at the Women in the World conference in New York on Thursday, Mrs Clinton said: "I did promote a no-fly zone, and I still believe we should have done a no-fly zone.
"I think we should have been more willing to confront Assad.
"Assad had an air force, and that air force is the cause of most of the civilian deaths.
"As we have seen over the years, and as we saw again in the last few days.
"I really believe that we should have, and still should, take out his airfields - and prevent him for being able to use them to use them to bomb innocent people and drop Sarin gas on them", she said to applause from the audience.
"I wish that the international community at large had been able to reign this in".
"Part of the reason Assad has been so dug in is because...his father destroyed a city that was a hot-bed of opposition to his rule.
"I mean literally massacred more than 10,000 people and almost seeded the ground so that nothing would grow there again".
It marks a change in tactic for the US president on whether it should take military action against the Syrian regime.
President Trump opposed any such action during the presidential campaign.
He criticised then-President Barack Obama for even considering such a move, tweeting: "There is no upside and tremendous downside".
President Obama, do not attack Syria. There is no upside and tremendous downside. Save your "powder" for another (and more important) day!— Donald J. Trump (@realDonaldTrump) September 7, 2013
But the strikes have seen wide support from many world leaders - including the UK, France, Germany and Australia.