The Russian president said his country would stand with the Assad regime in Syria if the US launches airstrikes.
The apparent threat came as the G20 summit ended with a public split, 11 of its members issuing a statement hinting at the need for US action against the Assad regime of its alleged use of chemical weapons.
Russia already supplies military aid to Syria, but the hint of more Russian backing in the event of a confrontation with the US sent jitters through financial markets worldwide.
Mr Putin also mocked Western leaders like US President Barack Obama considering intervening in Syria, suggesting that the majority of their electorates opposed any military action - including Prime Minister David Cameron for failing to persuade the Commons to back British involvement.
Mr Obama, meanwhile, compared the Syrian crisis to World War II, likening his country’s debate over intervention to the eventual American decision to support Britain against Nazi Germany.
The provocative remarks came at the end of a tense summit in St Petersburg where world leaders failed to narrow their differences over the Syrian crisis. » | James Kirkup in St Petersburg | Friday, September 06, 2013
