VIDEO: Barack Obama defends strategy to combat Islamic State

US president Barack Obama has laid out the most sweeping defence yet of his strategy to defeat Islamic State (IS), but he offered no US policy shift to confront what he called a “new phase” in the terrorist threat after a mass shooting in California.

In a rare Oval Office address, Obama sought to calm a US public increasingly jittery about the fight against Islamist militancy that once appeared to be waged overseas.

His remarks failed to quiet Republican critics who have long accused him of underestimating the militants’ strength and staying power.