Foreign Secretary Philip Hammond is told the UN that Britain will continue to bomb Islamic targets for "as long as it takes" and urged leaders to unite to fight against the extremist group.
At the UN General Assembly in New York, he said leaders must work together to "crush" IS and "banish its ideology from the face of the earth".
The parents of Aqsa Mahmood have criticised the government's decision to add their daughter's name to a UN sanctions list after she left the UK to join Islamic State.
Aamer Anwar, the family's lawyer, has said that Aqsa's parents believe the measure could mean other parents in similar situations not informing the authorities about any concerns they have over their children.
He added that parents Khalida and Muzaffar Mahmood also fear that sanctions could send a message to "brainwashed young people" who leave the UK for Syria, that they should stay there and not return home.
Mr Anwar said that Mr and Mrs Mahmood are very distressed over the government's announcement of the sanctions and think the move will make it even less likely they will see their daughter again.
Britain will continue bombing IS targets, Philip Hammond tells the UN as he urges leaders to unite to "crush" the extremist group.
It made for good headlines, but in a world where UK launches drone strikes on its citizens in Syria, are travel sanctions even a threat?
Government moves to tackle Islamic State recruitment by applying international sanctions to British citizens who joined the terror group.