UK's foreign secretary Philip Hammond today ruled out any alliance with Syrian President Bashar al- Assad to combat the Islamic State (IS) militants, who have unleashed havoc in Iraq and Syria, killing hundreds of people.
Former head of the British Army Lord Dannatt and former foreign secretary Sir Malcolm Rifkind had called for the move following the beheading of US journalist James Foley by IS militants.
"We may very well find that we are fighting, on some occasions, the same people that [Assad] is but that doesn't make us his ally," Hammond told BBC.
"It would not be practical, sensible or helpful to even think about going down that route," he added.
Even though the US and the UK came close to launching air strikes against the Assad regime last summer, there could be a case for collaborating with Assad in some way to ensure the defeat of IS, Rifkind had suggested.
But Hammond argued that Rifkind and Lord Dannatt were both wrong.
"I do not think that engaging in a dialogue with the Assad regime would advance the cause that we are all advocating here," Hammond said.
He added: "General Dannatt I heard talking about the adage that my enemy's enemy is my friend. I have said very often that one of the first things you learn in the Middle East is that my enemy's enemy is not necessarily my friend.
"We may very well find that we are aligned against a common enemy.
"But that does not make us able to trust them, it does not make us able to work with them and it would poison what we are trying to achieve in separating moderate Sunni opinion from the poisonous ideology of Isil [Islamic State] if we were to align ourselves with President Assad."
Hammond, however, did not rule out Britain supporting the US in launching air strikes against IS and confirmed that the UK was looking "sympathetically" at calls to provide arms to Kurdish peshmerga fighters who are at war with the IS.
He also said that Britain would consider supplying arms to the Iraqi government for the same reason once an inclusive, representative government was in place.
Meanwhile, British security forces are trying to identify the jihadist who had an English accent and appeared in footage of Foley's killing.
Unconfirmed reports suggest the man is from London or south-east England.
Hammond said authorities were "devoting significant amounts of resource to identifying the individual".
The government has defended its approach to extremists at home, following calls for a change in strategy prompted by the killing.
He said "significant powers" were available to deal with people planning to travel to Syria or Iraq to fight.
