UN aims to block jihadist recruits
David Cameron said the UN should "win the battle of ideas not just the battle of military might"
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Islamic State
David Cameron has said the UK is ready to "play its part" in fighting Islamic State, which he called an "evil against which the whole world must unite".
Speaking at the UN in New York, the prime minister said "past mistakes" must not be an "excuse" for inaction.
He spoke as US and Arab jets continued bombing Islamic State (IS) targets in Syria, after attacks began on Tuesday.
The UK cabinet will discuss plans for air strikes against IS in Iraq later, with Parliament due to vote on Friday.
In his UN speech, Mr Cameron said the Iraqi government had made a "clear request" for international military assistance against IS, which has taken control of large parts of Iraq and Syria in recent months.
He said this provided a "clear basis in international law for action".
Analysis
by Nick Bryant, BBC United Nations correspondent
David Cameron's address at the UN felt like a dress rehearsal for the speech he'll deliver in the House of Commons on Friday, and his target audience seemed to be parliamentarians as much as diplomats in the hall.
Other than a few cursory words about Middle East peace, Ukraine and the Ebola outbreak in West Africa, it was devoted almost exclusively to making the case for British air strikes in Iraq.
Referring to the war there a decade ago, a conflict lodged so firmly in the minds of parliamentarians, he said that past mistakes should not become an "excuse for indifference or inaction".
He was also careful to spell out the legal case for air strikes in Iraq, a touchier issue in Westminster than it is in New York.
Mr Cameron said he did not believe Western countries should send ground troops in to fight, but there was a place for action by armed forces.
As well as air strikes, he said Western forces could equip, train and support those who are "fighting on the front line for their societies and for their countries and for their freedom".
He said IS, also known as Isil and Isis, had killed people of "every faith and none" and had "murderous plans to expand its borders well beyond Iraq and Syria and to carry out terrorist atrocities right across the world".
A new IS video purportedly shows new recruits
Mr Cameron said it was "right" to learn lessons from the past - especially from the 2003 invasion of Iraq - but leaders must not be "frozen with fear".
"Isolation and withdrawing from a problem like Isil will only make matters worse," he said.
"We must not allow past mistakes to become an excuse for indifference or inaction."
He also said:
- the international community should support "representative and accountable" Middle Eastern governments to fight IS - not go "over their heads"
- "partners" in the region could include Iran - though he met the Iranian president on Wednesday and said there were "severe disagreements" between the two countries
- it was "dangerously misguided" to suggest working with the Assad regime in Syria, which is also fighting IS
- all nations must stop "so-called non-violent extremists from inciting hatred and intolerance"
'Network of death'
Mr Cameron said IS had recruited fighters from around the world, including 500 from Britain.
One of these Britons "almost certainly" killed the two American journalists and the British aid worker whose beheadings featured on IS videos posted online in recent weeks, he said.
The UN Security Council has adopted a
binding resolution compelling states to prevent their nationals joining jihadists in Iraq and Syria.
US President Barack Obama chaired the session and called for global efforts to dismantle the IS "network of death".
He said more than 40 countries had offered to join the coalition against IS, which is made up of well-armed Sunni Muslim militants who aim to set up a hardline caliphate.
The US started bombing IS targets in Iraq last month and began bombing in Syria on Tuesday.
It said Saudi Arabia, the United Arab Emirates, Jordan, Bahrain and Qatar had all "participated in or supported" the Syria strikes, which the US military said had targeted vehicles, arms dumps and small-scale oil refineries.
The UK is considering joining the US in carrying out air strikes in Iraq
Buildings in Raqqa were damaged by the US-led air strikes in Syria
Labour and the Liberal Democrats are supporting the plan for air strikes in Iraq.
BBC deputy political editor
James Landale said the government was "confident" of winning Friday's vote - but it did not propose military action in Syria due to the "the legal impediments of acting there without the support of the Assad regime".
However, former UK Attorney General Dominic Grieve told BBC Newsnight the Iraqi government's request for help could make it possible for the UK to take military action in Syria without breaching international law.
He said there was evidence that some attacks were "spilling over the border" from Syria into Iraq, so the UK could use "reasonable, necessary and proportionate means" to help Iraq defend itself.
He said it might also be possible to make a legal case for intervening in Syria under the "doctrine of humanitarian necessity" to protect people from IS genocide.
http://www.bbc.com/news/uk-29357116