Muslim leaders in the UK have issued a fatwa condemning British jihadis who fight alongside the Islamic State terrorist group, saying they are "betraying their own societies".
The fatwa, which The Sunday Times (£) said had been issued by imams, is the strongest condemnation yet of Britons joining Islamic extremists by the Muslim community.
It comes as Britain's terror threat was hiked from "substantial" to "severe" in response to fighting in Iraq and Syria, and the seemingly growing influence of the Islamic State terror group.
Home Secretary Theresa May said the new alert level rated the risk of an attack on the UK as "highly likely", although she said there was no evidence to suggest one was "imminent".
British Muslims who ally with Islamic State are 'heretics', the fatwa said
Six senior Islamic scholars have endorsed the fatwa, describing Britons allied to Islamic State cells as "heretics".
"There is no doubt that President Assad’s regime in Syria is oppressive, unjust and brutal, and has committed numerous atrocities against its own people," the fatwa says.
"The same is true of the so-called Islamic State (IS) or self-styled Caliphate, it is an oppressive and tyrannical group.
"By murdering prisoners of war, journalists and civilians, including mosque imams who refused to endorse their campaign, and by enslaving the women and children of their opponents, ISIS has violated international agreements such as the Geneva Conventions and conventions on slavery that everyone, including Muslims, have signed up to. God says in the Qur’an, 'Believers, fulfil your covenants!'”
Issued by a learned Muslim scholar, a fatwa is an edict that may concern any aspect of Islamic life.
Technically it cannot be revoked and dies only with the person it is imposed on.
The term fatwa became famous in the West in 1989 after the author Salman Rushdie was forced into hiding following a ''death fatwa'' issued by Ayatollah Khomeni, then Supreme Leader of Iran, on the grounds that his book, The Satanic Verses, had ''insulted'' Islam.
Former Liberal Democrat leader Lord Ashdown has hit out at David Cameron over his response to the threat posed by British jihadis in a sign of the junior coalition partner's unease about plans to tighten anti-terror laws.
The prime minister will make a Commons statement tomorrow on measures to tackle the danger from IS extremists, with his Lib Dem deputy Nick Clegg insisting that the changes will need careful consideration and must be based on evidence.
Mr Cameron has said action is needed to close "gaps in our armoury", including new legislation to make it easier to take people's passports away to prevent them from travelling to Iraq and Syria.
The proposals come in response to the raising of the terror threat level in the UK, with experts warning that an attack was "highly likely".
But Lord Ashdown, writing in The Observer, said politicians should not act as "cheerleaders" for the demands of the intelligence and security services. And he warned that the Prime Minister's rhetoric risked alienating moderate Muslims.
He said Tory ministers - including Mr Cameron - had used the decision to raise the terror threat level "to tell us how frightened we should be and why this required a range of new powers for them to exercise".
Lord Ashdown said the threat of terrorism had been faced before "effectively, without panic and without a whole new range of executive powers that could endanger our liberties".
He said: "Of course, in these circumstances, the police and the security services will lead the clamour for more powers. They are charged by us to maintain our safety.
"It is natural they should want the most powerful weapons to enable them to do so. That's their job. But it is the job of politicians to act, not as cheerleaders for those demands, but as jealous protectors of our liberties who measure any demand for their reduction against necessity, supported by evidence."