President Barack Obama has announced that he will authorise targeted strikes against Islamist militant convoys in northern Iraq if they threaten US facilities and personnel there, as well as continuing humanitarian air drops to Iraqis under threat from fighters from Islamic State (IS) militants.br br He said US intervention was justified by the threat and a request for support from the Iraqi government. However, he said US troops would be not be sent back to Iraq.br br Mr Obama said the US would act "carefully and responsibly to prevent an act of genocide".