It comes as the death toll of the Algerian oil refinery crisis rose to at least 81 last night.
Mr Cameron said the attack was a stark reminder of the continuing terrorist threat and vowed to use Britain's chairmanship of the G8 this year to ensure it was at the top of the international agenda. He said: "This is a global threat and it will require a global response. It will require a response that is about years, even decades."
"It requires a response that is patient and painstaking, that is tough but intelligent, but above all has an absolutely iron resolve and that is what we will deliver over these coming years."
He confirmed three Britons had been killed in the Algerian terrorist attack, with three more Britons as well as a British resident feared dead. Amongst them are two Scots who have yet to be confirmed dead or alive.
Mr Cameron is due to make a further statement to the Commons today.
Algerian special forces stormed the refinery on Saturday to end the four-day siege. The Government said then that 32 militants and 23 hostages were killed, but that the death toll was likely to rise.
At least 25 bodies were found at the Al Imenas oil complex yesterday, according to reports. State troops have also now recovered a terrorist arsenal from the oil refinery, which is due to re-open this week.
Moktar Belmoktar, the veteran jihadist leader, has claimed responsibility for the attack and threatened more unless the French offensive against militants in neighbouring Mali stops. His al Qaeda group, which calls itself "those who sign in blood", said there were 40 militants involved in the gas plant siege from "several Islamic countries, even from Western countries".
Mr Cameron said what was now faced in North Africa was an extremist, Islamist, al Qaeda-linked terrorist group similar to those in Pakistan and Afghanistan.
"It is linked to al Qaeda, it wants to destroy our way of life, it believes in killing as many people as it can. We need to work with others to defeat the terrorists," he added.
He refused to criticise the hardline tactics of the Algerian Government, which from the start ruled out any negotiation with the terrorists. He insisted: "The responsibility for these deaths lies squarely with the terrorists who launched these vicious and cowardly attacks."
Foreign Secretary William Hague branded the terrorists cold-blooded murderers and said reports seven hostages had been executed could well be true.
A video is said to show Belmoktar claiming he was prepared to negotiate with Western and Algerian leaders if the French offensive in neighbouring Mali were stopped.