Aseel Muthana, 18, from Cardiff travelled to Syria in February last year to connect with his brother who had already gone to Syria to join the ISIS terror group and is also on the banned list.
Muthana has boasted of being ready to "die for the cause" and promoted jihad in media interviews. Last year, the teenager described seeing "martyrs" to the ISIS 'cause' and said he does not plan to come home.
His addition to the UN al-Qaeda sanctions regime list was expected to be approved alongside four other British extremists earlier this week but was temporarily delayed under the UN sanctions.
Under the UN sanctions, Muthana's assets will now be frozen and a travel ban imposed on him.
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The "notorious fighters" had been plotting attacks in Britain and elsewhere and posed a "real threat" to innocent people, the Telegraph quoted a senior government official as saying.
On the Consolidated United Nations Security Council Sanctions List, Muthana is described as a "foreign terrorist fighter with Islamic State in Iraq and the Levant" and wanted by authorities in the UK.
The UN sanctions regime was set up to tackle suspected al-Qaeda terrorism and extended to ISIS.