A Muslim police officer was excused duty guarding Israel's embassy for safety reasons, Scotland Yard has said.
Paul Stephenson says the move was not down to political correctness
The Sun newspaper said the officer was reassigned on "moral grounds" as he objected to Israeli actions in Lebanon.
The Diplomatic Protection Group officer, named as Pc Alexander Omar Basha, had Lebanese relatives.
But Metropolitan Police Deputy Commissioner Paul Stephenson said the move followed a risk assessment and was "not about political correctness".
The decision to excuse the officer has been attacked by some former police officers and politicians, while being defended by groups representing officers.
Met Commissioner Sir Ian Blair ordered an urgent review into the matter.
Mr Stephenson said: "At the height of the Israeli/Lebanon conflict in August this year, the officer made his managers aware of his personal concerns which included that he had Lebanese family members."
He said that following a risk assessment "and not because of the officer's personal views whatever they might have been", a temporary decision was made not to deploy Pc Basha to the Israeli embassy.
"Our priority is making sure that any officer we deploy can have their mind on the job and make sure they discharge effectively and efficiently.
"That's what a risk assessment is about, it is not about political correctness and we do not allow officers to pick and choose their deployment on the basis of their personal views."
The Association of Muslim Police Officers said it had been a "welfare issue" not a political one - with the officer having a Syrian father and a Lebanese wife.
The association said Pc Basha had asked to be excused from his duties because he felt "uncomfortable and unsafe".
Superintendent Dal Babu, from the association, told BBC News Pc Basha was now back on diplomatic protection group duties and that "if an incident happens at the Israeli embassy he will deal with it".
Supt Babu accepted that excusing officers from assignments because of moral beliefs would be unacceptable.
"I think that we're going down a very, very slippery slope if we then start having postings based on individual officers' conscience," he said.
Lord Mackenzie, a former president of the Police Superintendents' Association of England and Wales, said the move sounded like "a step too far".
"What we don't want is a situation where one particular section of the community is given special reasons for not performing duties because that will simply alienate the rest."
The Metropolitan Police Authority, which has also asked for a report, said officers often had to undertake duties where the subject conflicted with their personal beliefs.
But MPA member Peter Herbert said the row was a "ridiculous fuss about nothing" and attacked Sir Ian over an "unwise judgement" on opting so quickly for a review.
"From a security point of view, the Met would be seriously criticised if this guy has relatives in Lebanon and his picture was used around the world to demonstrate the irony about having a Muslim defending the Israeli embassy in the UK."
Glen Smyth, chairman of the Metropolitan Police Federation, which represents rank-and-file officers, said just one two-hour slot outside the embassy had been affected.
The officer had not refused to do duties and had made a simple request which it was "fairly sensible" to grant, Mr Smyth said.
Lord Janner, former president of the Board of Deputies of British Jews, said it was a "grave error" to allow a police officer to avoid his duty.
"To start this system where somebody can say look I don't like this because of my own political belief or religion is a mistake because if this grows it can harm the system."
The Israeli embassy in London, meanwhile, said it was confident the Met Police would find "a satisfactory solution to this particular problem".