Cameron also said that he had a telephonic conversation with US President Barack Obama on Tuesday over concerns after forces loyal to Gaddafi launched more air strikes, and added that both of them had discussed preparations for future options over the matter.
"We have got to prepare for what we might have to do if he [Gaddafi] goes on brutalising his own people," the BBC quoted him, as saying.
"I had a phone call with President Obama this afternoon to talk about the planning we have to do in case this continues and in case he does terrible things to his own people. I don't think we can stand aside and let that happen," Cameron added.
Number 10 said that leaders of both parties agreed to the objectives of securing an "immediate end to brutality and violence", and the departure of Gaddafi, the report said.
"The Prime Minister and the president agreed to press forward with planning, including at NATO, on the full spectrum of possible responses, including surveillance, humanitarian assistance, enforcement of the arms embargo, and a no-fly zone. They committed to close co-ordination on next steps," a Downing Street spokesman said.