New York - The UN political chief on Tuesday urged the world's nations to share information about airline passengers as part of a stepped up response to the growth of "transnational terrorism" sparked by the Islamic State group's expanding areas of attack.Jeffrey Feltman also told the UN Security Council that it is "critical" to improve the global response to "foreign terrorist fighters" leaving Syria and Iraq, even though many are still in conflict zones.He was briefing the council on Secretary General Antonio Guterres' latest report on ISIS - also known as ISIL and Daesh. It said European member states have reported that between 15% and 40% of their nationals and residents who travelled to Iraq and Syria to fight have returned - and some governments highlighted a rising number of female returnees."A proportion of those returning present a significant threat and are facing appropriate legal and control measures," the secretary general's report said. "Other returnees are reported to have become disillusioned with the fighting and the distorted ideology of ISIL and therefore represent a lower threat."In a separate report to the Security Council circulated late on Tuesday, a panel of experts that monitors sanctions against ISIS said it has received various estimates of the current number of fighters for the extremist group. They range from 12 000 to 20 000 in Syria and Iraq, to 33 000 fighters in the wider Middle East, "including 15 000 foreign terrorist fighters", the report said.In December, the Security Council urged all 193 member states to address "the gravity of the threat" posed by ISIS by adopting laws and sharing intelligence, biometric- and biographical data and financial information related to extremist groups and by requiring airlines operating in their territories to provide advance information on passengers to national authorities.According to the report, only 56 nations have shared advance passenger information to date, and implementation of the council's call for countries to share passenger name records "continues to be uneven".'Significant vulnerability'While some countries have voluntarily provided passenger name records from ocean and sea traffic and cruise ships, "a lack of appropriate regulation continues to represent a significant vulnerability", the report said.Feltman reiterated that although the Islamic State group's income and the territory under its control are shrinking, it "still appears to have sufficient funds to continue fighting". Moreover, he said, the group has expanded its attacks from Iraq and Syria to their neighbours and continues encouraging followers in Europe, Africa and elsewhere to perpetrate attacks.The United States, France and Britain, all part of the coalition fighting ISIS, reiterated their determination to defeat the extremist group.US Ambassador Nikki Haley told the council in closed consultations after Feltman's briefing that while ISIS extremists are losing ground, the United States will maintain pressure on its safe havens, continue to restrict its finances, and work with partners to take aggressive action where possible to defeat the group and its global threat, according to a US Mission spokesperson who was not authorised to speak publicly.Britain's deputy UN ambassador, Peter Wilson, said that "Daesh is on the back foot" and the next step for the 68-country coalition is to attack the extremist group in its headquarters in the Syrian city of Raqqa and in Iraq's second-largest city, Mosul.French Ambassador Francois Delattre said collective efforts "have produced significant results with important military and financial setbacks for Daesh over the past year"."It is crucial that the international community keep its efforts on all fronts, military, financial and others, so that we get to the eradication of Daesh," Delattre added.