Four high-profile UK jihadists fighting or recruiting for Islamic State militants in Syria are to be subjected to UN sanctions, at the UK's request.
The UN's updated sanctions list named the four as Omar Hussain from High Wycombe, Nasser Muthana from Cardiff, Aqsa Mahmood from Glasgow and Sally-Anne Jones from Chatham in Kent.
They will face a travel ban and a freeze of their assets.
The move is a new tactic to stem the flow of recruits to the IS group.
At least 700 Britons have travelled to support or fight for jihadist groups in Syria and Iraq, according to British police. About half have since returned to the UK.
It is the first time since 2006 that Britain has submitted names to the UN sanctions regime, which was set up to tackle suspected al-Qaeda terrorism and extended to IS.
A government official said the move was intended to send out a deterrent message.
One name submitted to the sanctions committee is still to be approved and more are expected to be put forward.
Jones has written on Twitter that she is "laughing out loud" at receiving the travel ban, but her latest account has since been suspended by the company.
The family of Mahmood described the move as "useless grandstanding" by David Cameron.
By Dominic Casciani, home affairs correspondent, BBC News
Financial sanctions lists are arguably as symbolic as they are practical. Unusually, they put the names of suspects in the public domain, even if they have not faced arrest, charge and prosecution.
Although this is the first time the UN list has been used against Britons in Syria, the broadly comparable UK Treasury list has been used to target two other men.
The aim is disruption.
Banks and other institutions prevent named suspects getting at any cash they have, receiving funding and moving it around. On that level, the sanctions obviously perform a job.
But the effect on any target inside IS territory, who has no intention of leaving or using their British bank card, is obviously limited.
IS recruits bring plenty of cash, knowing they won't be able to get hold of what they leave behind.
Dossiers of evidence were submitted to show the Britons were "participating in the financing, planning, facilitating, preparing, or perpetrating of acts or activities" related to IS.
Uploading bomb-making instructions to social media was among the activities.
The government official said: "We will absolutely go after people who fight for Isil [also known as IS] and are threatening our country."
The four named by the government have been widely reported by the British media for their alleged IS activities.
- Aqsa Mahmood, 21, has been accused of recruiting three London schoolgirls to join IS - something her parents have denied.
- Nasser Muthana, 21, is accused of appearing in videos showing beheadings, although his father said it was not him.
- Sally-Anne Jones, 46 - reportedly a former rock musician - has been dubbed the "punk jihadi" by the tabloid newspapers and is accused of recruiting for the group.
- Omar Hussain, 28, a former supermarket security guard, has appeared in a propaganda video and was interviewed on Newsnight.
Aqsa Mahmood travelled to Syria in 2013 and is believed to have married an IS fighter.
She is described on the list as being a recruiter for the militant group and a key figure in the al-Khanssaa brigade - a female brigade within IS, established in the Syrian city of Raqqa to enforce its interpretation of Sharia law.
Nasser Muthana and Omar Hussain travelled to Syria in 2013 and 2014 respectively and are both described as IS fighters.
Sally-Anne Jones, who was married to Junaid Hussain, a British jihadist killed in a Syria drone strike, travelled to Syria with her husband in 2013 and is on the list for being a recruiter for the group.
Aamer Anwar, the Mahmood family's lawyer, said they were "horrified and distraught".
"They believe this is no more than useless grandstanding by the prime minister," he said.
"In relation to the financial aspects, freezing of assets will have no impact at all on somebody like Aqsa Mahmood, who had no assets.
"But it will also have no impact, they believe, on young teenagers who want to go off and fight for Isis.
"It's hardly going to stop them or deter them that the prime minister wants to freeze their bank accounts or their pocket money."
He said the family was more concerned about the travel ban.
"They've always hoped that one day their daughter one day would see sense, that Isis is no more than a twisted perverted distortion of Islam - it's a death cult," he said.
"And that she would break with them and one day come home.
"The idea of a travel ban is literally the British government washing their hands of their own citizens and saying: 'It's Syria's problem now'."
Muthana's father, Ahmed, said that as far as he knew his son, who studied medicine before leaving Cardiff in 2013, did not have any money to freeze.
The UN list contains the names of 72 organisations and 231 individuals. British nationals Abu Hamza al-Masri, currently serving a life sentence in prison after being found guilty of supporting terrorism, and Syrian-born Mohammed al Ghabra, 35, from east London, who has been linked to al-Qaeda, were already on the list.
'Hearts and minds'
The announcement of the sanctions comes as the prime minister joins other world leaders at the UN General Assembly in New York.
The government is also to spend an extra £10m on a new unit to counter propaganda from IS militants and is establishing a new committee of senior ministers to focus on the threat from the group.
A British official said Mr Cameron believes "we can and must do more to win the battle for hearts and minds".
The new unit will be based in London but with links across the Arab world to try to counter the extremist message.