The chair of the U.N. committee monitoring sanctions against extremists says the Islamic State group is looking to increase revenue from taxation, smuggling antiquities "and potentially kidnap for ransom" following the loss of some territory and destruction of oil facilities.

New Zealand's U.N. Ambassador Gerard van Bohemen told the U.N. Security Council on Thursday that the Islamic State group is not short of arms or fighters.

While recent reports indicate that the flow of recruits is slowing, he said, "estimates suggest that upwards of 30,000 foreign terrorist fighters have traveled to Iraq and Syria to date."

Van Bohemen said the threat from IS is also expanding geographically, and as pressure increases on its territory in Syria and Iraq, foreign fighters are seeking to return home.