Five Britons who have joined ISIS and attempted to recruit others online have been placed on the UN sanctions list.
The British Islamic State members sanctioned by the UN – profiles http://t.co/5DGWT7aIst
The list includes Sally-Ann Jones, a 46-year-old convert to Islam from Kent; 28-year-old Omar Hussain from High Wycombe, Buckinghamshire; Nasser Mutthana, a 21-year-old from Cardiff; and Aqsa Mahmood, a 21-year-old from Glasgow.
On Thursday, it was revealed that Nasser Mutthana's brother, 19-year-old Aseel, from Cardiff, in Wales, was also placed on the list.
He is believed to be in ISIS' self-declared capital in Raqqa, and has appeared on ISIS propaganda videos.
While the UN sanctions list was initially designed to curb the influence of jihadis aligned to al-Qaeda, the British government proposed the Britons be added to the list as a way to deter others from joining ISIS.
Those on the list face travel bans and having their assets frozen.
The Britons are said to have used social media as a way to recruit Muslims from the West to join the militant group.
Mahmood has also been listed as a "key figure" in the Al-Khansaa brigade, a specialist, all-female group designed to "enforce ISIS's interpretation of Sharia law".
Downing Street said the international sanctions will work in conjunction with domestic deterrents, such as seizing passports.
"The prime minister has been absolutely clear that we will do all we can to stop British citizens from going to fight for ISIL and that foreign fighters should face consequences for their actions," a spokesperson for No 10 told BuzzFeed News.
"It also sends a clear deterrent message to those thinking of going to fight for ISIL. We will continue to consider whether more individuals should be subjected to these sanctions."
Following the decision, a Twitter account believed to belong to Sally-Ann Jones mocked the prime minister.
Just found out from a article that David Cameron has put me on a UN Sanctions list as i lol @ England for giving me a travel ban :)
The British government estimates that around 700 Britons have travelled to Syria to fight with militant groups since the civil war began.
While the British government intends to use measures such as the sanctions list to prevent other Britons from travelling to Syria, some experts have expressed doubt over how effective it will be.
"For those who are already sympathetic to Islamic State, I think a move like this could actually galvanise them," Shiraz Maher, a senior fellow at the International Centre for the Study of Radicalisation, told BuzzFeed News.
"They see things like this and feel their compatriots in Islamic State are becoming important and meaningful, to such an extent that there's a need to have them internationally designated."
He added: "All of that feeds into the sense that you can go from being a nobody in the West to being an important figure in Islamic State – so important that you catch the attention of David Cameron, the United States, and UN."
Cameron met with world leaders at the United Nations in New York earlier this week.
Discussions included the conflict in Syria and how to counter ISIS propaganda online.