Reuters, London :Only one in 20 Russian air strikes in Syria are aimed at Islamic State targets, Britain’s defence secretary said on Saturday, warning that Vladimir Putin was instead killing civilians to shore up President Bashar al-Assad.Russia earlier this week announced its decision to launch strikes on Syria, in a dramatic escalation of foreign involvement in a civil war more than four years old.It bombed the country for a third straight day on Friday, but it has mainly hit areas held by rival insurgent groups rather than the Islamic State fighters it said it was targeting, drawing an increasingly angry response from the West.British Prime Minister David Cameron said on Saturday Putin was making the situation worse by helping the “butcher Assad” and urged world leaders to work towards a political transition in Syria.In an interview with the Sun newspaper, British Defence Secretary Michael Fallon said the vast majority of Russian air strikes were not aimed at the militant group at all.