The UK, in line with a United Nations Security Council resolution, has frozen the assets of Qadhafi and his family and barred them from entering the UK.
Mr Cameron said: “All of this sends a clear message to this regime: it is time for Colonel Qadhafi to go and to go now.
“There is no future for Libya that includes him.”
The Prime Minister, speaking inside Downing Street, also said that he was “delighted” at the success of a second special forces-led operation to rescue oil workers stuck in the remote Libyan desert.
The PM welcomed the safe extraction of another 150 civilians - including an unspecified number of UK nationals - in three RAF Hercules transport planes to Malta.
Obviously Libya is a country in complete chaos and so it is difficult to arrange these things. But it was the right thing to do and I pay tribute to the very brave pilots and armed services personnel who managed to help so many British citizens back to safety and I am delighted they have been able to do that.
The UN Security Council agreed to refer the brutal repression of the popular uprising to the International Criminal Court as well as approving an asset freeze, travel ban and arms embargo.
The UK asset freeze on Mr Qadhafi, five of his children “and those acting on their behalf” was announced by Chancellor George Osborne after being formally approved at a Privy Council meeting with the Queen at Windsor Castle.
Speeches and transcripts: PM’s interview on Libya