Lord Ashdown has attacked the coalition's handling of the crisis in Syria, accusing ministers of engaging in Iraq War-era diplomacy.
The former Liberal Democrat leader said the West's rhetoric had made it easy for Russia and China to dismiss calls for action against president Bashar Assad.
The comments came amid reports of fresh violence in Homs province, where more than 30 people are thought to have died yesterday.
Lord Ashdown told BBC Radio 4's World at One: "I think this has not been clever diplomacy to get to where we are.
"Instead of learning the lessons of Libya - where we tried to put the regional coalition out front and the West backed it and were careful not to use 'regime change' - in Syria we have charged out front, all the West, dressed in their shining suits of armour, as though the days of Iraq were still there.
"We have demanded regime change from the Russians, whose only friend in the Middle East is Assad.
"I don't think that is wise diplomacy."
He went on: "The product of not learning the lessons of Libya is that we made it as easy as possible for China and for Russia to say no, saying this was modern imperialism, which of course it is not.
"Everybody knows that in the end Assad must go but we knew that about Gaddafi too - we were wise enough not to say so and achieve it by other means.
"I just think that in our thinking about how to handle these things we have gone backwards to the days of Iraq as though the West still had power that it had in those days, which it does not."
Lord Ashdown played down Foreign Secretary William Hague's comparison between Syria and the Bosnian war in the 1990s.
The peer, who served as high representative to Bosnia for four years, said there had been the possibility of Western military intervention at that time, but not now.
He urged the Government to engage in "canny diplomacy" by stressing the humanitarian crisis engulfing Syria rather than the need for regime change.
The ex-Royal Marine also warned of the risk that the situation could lead to a wider regional ethnic conflict between Sunni and Shia.