British cargo planes carrying drinking water and tents have dropped emergency supplies over Iraq, focusing attention on the Yazidi community, a minority group besieged by Islamic militants in the Sinjar mountains in northern Iraq.
American forces have been carrying out airstrikes to support Kurdish and Iraqi forces fighting the militants. But with media replete with stories of suffering and atrocities, Britain's government is being called to account.
"These people are being beheaded ... And our only response is to drop some food or water on them," he said.
London Mayor Boris Johnson, a prominent member of Cameron's Conservative Party, has also urged Britain to do more, writing in the Daily Telegraph that action is needed to prevent "the Ebola-like spread of the fanatics."
Ex-Army chief Gen Richard Dannatt told the BBC today that it may be necessary to put British troops on the ground to direct air support.