IS: David Cameron defends Iraq air strike strategy
David Cameron has defended efforts to combat Islamic State (IS) militants in Iraq using air strikes, saying the UK's military approach is not "simplistic".
The prime minister told the BBC's Andrew Marr Show that air strikes were "part of a comprehensive strategy".
Some commentators have suggested ground troops would also be necessary.
RAF jets have begun carrying out combat missions over Iraq after Parliament voted by 524 votes to 43 to take action against IS in Iraq.
The UK's military presence is part of a US-led coalition of about 40 countries, including Arab states, that has vowed to destroy IS, which controls large parts of north-eastern Syria and northern Iraq.
At least two British hostages are thought to be being held by the group - journalist John Cantlie and taxi driver Alan Henning, who had been delivering humanitarian aid to Syria.
A video showing the killing of a third Briton, aid worker David Haines, was released earlier this month.
'Psychopathic terrorist killers'
IS - which is also known as Isis and Isil - captured broad swathes of Iraq in June, declaring a caliphate in areas it controls in Syria and Iraq.
The group pursues an extreme form of Sunni Islam and has persecuted non-Muslims and Shia Muslims, becoming known for brutal tactics such as beheading soldiers, Western journalists and aid workers.
Mr Cameron said: "When you face a situation with psychopathic terrorist killers in Syria and Iraq, who have already brutally beheaded one of our own citizens, who have already launched and tried to execute plots in our own country to kill and maim innocent people, you have got a choice.
"We can either stand back from all of this... and say 'this is too difficult, it's too complicated, let's let someone else try to keep our country safe'... or we take the correct decision to say 'let's have a full, comprehensive strategy'."
Respect MP George Galloway has warned that the nature of the IS positions mean many civilians may be killed.
And Lord Richards of Herstmonceux - a former head of the UK military who stepped down as chief of the defence staff last year - told the Sunday Times: "We have to view it as a conventional campaign, which means you have to have boots on the ground.
"This doesn't mean they have to be Western, but you do have to have an army to contain, defeat and destroy. You can't do it by air alone."
He also told the paper: "You can't possibly defeat Isis by only attacking them in Iraq.
"How the hell can you win the war when most of your enemy can end up in a country you can't get involved in?"
But, rejecting these criticisms, Mr Cameron said the UK's strategy was "not some simplistic 'drop a bomb from 40,000 feet and think you can solve a problem'" approach.
He said: "We are not trying to defeat Isil from the air alone. We believe you do need troops on the ground - but they should be Iraqi troops, they should be Kurdish troops."
The prime minister said the use of air strikes was "one part of a comprehensive strategy to build an Iraq that has a democratic, inclusive government for everyone and, in time, Syria needs exactly the same thing".
He added: "We support what the Americans and the five Arab nations have done in Syria. We have a Syria strategy - which is to build up the Free Syrian Army, the Syrian National Coalition, to achieve a political transition in Syria."
Meanwhile, Defence Secretary Michael Fallon warned that this was "not a 24-hour or 48-hour campaign".
He said: "This isn't going to be a weekend campaign.
"This is a campaign that is going to take weeks and probably months to push Isil back, out of the town and villages in western Iraq that they've captured."
When asked whether the British military presence was likely to move to Syria, Mr Fallon said: "We think Isil will have to be defeated in both countries, but first we're going to see how we can help best in the campaign in Iraq.
"Then, if we need to return to Parliament and ask for fresh authority, there would then be a further debate and a further vote. But we have not taken that decision yet."
- Formed out of al-Qaeda in Iraq (AQI) in 2013, IS first captured Raqqa in eastern Syria
- It captured broad swathes of Iraq in June, including Mosul, and declared a "caliphate" in areas it controls in Syria and Iraq
- Pursuing an extreme form of Sunni Islam, IS has persecuted non-Muslims such as Yazidis and Christians, as well as Shia Muslims, whom it regards as heretics
- Known for its brutal tactics, including beheadings of soldiers, Western journalists and aid workers
- The CIA says the group could have as many as 31,000 fighters in Iraq and Syria