PM: returning jihadists are a huge threat to UK
The Prime Minister insisted the prospect of battle-hardened jihadists returning to the UK was a "real threat to our country".
But he denied that the Government was restoring diplomatic links with neighbouring Iran in a bid to win Tehran's help to quell the spread of Islamic State of Iraq and the Levant (Isis) militants.
Mr Cameron said: "No one should be in any doubt that what we see in Syria and now in Iraq in terms of Isis is the most serous threat to Britain's security that there is today.
"The number of foreign fighters in that area, the number of foreign fighters including those from the UK who could try to return to the UK, this is a real threat to our country.
"We will do absolutely everything we can to keep our people safe. That means stopping people from going, it means arresting people who are involved in plots, it means focusing our security, our policing, our intelligence effort on to that area of the world, on to those people."
The comments came after Foreign Secretary William Hague said the "circumstances are right" to reopen the embassy in Tehran, which shut after being ransacked by a mob protesting against sanctions in 2011.
The move comes as more evidence emerged of brutal executions by Isis. And yesterday there were claims that pro-government Shiite militiamen have killed nearly four-dozen Sunni detainees after insurgents tried to storm a jail north east of Baghdad and free them, police say.
The Iraqi military claimed the inmates were killed when the attackers shelled the facility.