The Obama administration is treading cautiously on Syria after what it sees as Washington's past errors in the Iraq invasion and occupation, Vice President Joe Biden said. Insisting that President Barack Obama and his team had helped restore America's image in the world, Biden told Rolling Stone magazine in an interview published Thursday that "we don't want to blow it like the last administration did in Iraq, saying 'weapons of mass destruction.'" Iraq's alleged weapons of mass destruction, cited by George W. Bush's administration as the main motive to launch the US-led invasion in 2003, never surfaced after the fall of Saddam Hussein's regime. The US government cited for the first time two weeks ago the Syrian regime's possible use of chemical weapons against its own people, but Obama stressed that there was insufficient proof to determine whether a "red line" had been crossed. "We know that there have been traces found of what are probably chemical weapons," Biden said. "What we don't know yet -- and we're drilling down on it as hard as we can -- is whether they were accidentally released in an exchange of gunfire or artillery fire, or blown up or something." He also stressed that it remained unclear who owned the weapons and used them at which point in time. "We don't know for certain whether they were used by some of the opposition, including the radicals who have aligned themselves with Al-Qaeda," the vice president added. "It's probable, but we don't know for certain, that they were used by the regime." And he stressed that once the use of the chemical weapons has been verified, Obama would likely make a "proportional response in terms of meaningful action," without providing further details. "We also believe that no matter how this ends, there is going to be political unrest in Syria for some time to come," Biden said, calling for an "inclusive, non-sectarian" government with functioning institutions once President Bashar al-Assad steps down or is removed from power. "The one lesson we learned from Iraq and the last administration is... How can I say it? In managing the affairs in Iraq, they destroyed every institution. There was no structure left. There wasn't even a Department of Public Works. "And we know we can fix that, if we're willing to spend a trillion dollars and 160,000 troops and 6,000 dead, but that we cannot do," he added, in reference to the US troop deployment and toll in blood and treasure in Iraq. His remarks were some of the clearest yet from a currently serving top US official linking the decision to invade Iraq a decade ago and Washington's current hesitation toward Syria, where a civil war has killed more than 70,000 people in just over two years. Obama said Tuesday that before acting, Washington must first establish exactly who had used chemical weapons and when, in an apparent reference to the flawed intelligence that led America into war with Iraq. "I don't make decisions based on 'perceived,'" he said, when asked about perceived violations of US red lines. "I can't organize international coalitions around 'perceived.' We've tried that in the past, by the way, and it didn't work out well."