Body armour and counter-explosive equipment are among high-tech items being considered as part of a shipment of military hardware to be sent to Iraq to bolster out-gunned anti-IS forces.
Mr Cameron said it was “hardly surprising” that voters were wary of any re-engagement in the country, more than a decade after the US-led invasion which ended in the present chaos.
But while it was right not to “send armies to fight or occupy”, he wrote in the Sunday Telegraph, the threat posed by the Islamists was so great that some military intervention was fully justified.
If IS succeeded in creating a wide-ranging caliphate encompassing several countries across the region “we would be facing a terrorist state on the shores of the Mediterranean and bordering a Nato member.
“This is a clear danger to Europe and to our security,” he wrote.
“It is a daunting challenge. But it is not an invincible one, as long as we are now ready and able to summon up the political will to defend our own values and way of life with the same determination, courage and tenacity as we have faced danger before in our history.
“That is how much is at stake here: we have no choice but to rise to the challenge.”
The continued threat was underlined by reports of a fresh massacre of members of the Yazidi religious minority at the hands of jihadists, despite continued US air strikes against militant positions. Officials and eyewitnesses said 80 men were killed and their wives and children abducted.