The United States is to implement tougher security measures on travellers from Europe and US-allied countries in order to better track Islamist militants who hold Western passports, according to US officials.
Officials revealed that the new screening procedures are to be imposed because of concern over the number of citizens from "visa-waiver" countries that have flocked to Syria to fight for jihadist groups, and the ease at which some can travel across Europe and even to the United States.
Homeland Security Secretary Jeh Johnson announced in a statement obtained by the Washington Post that the security measures are required "to learn more about travellers from countries from whom we do not require a visa."
The new measures are to make millions of travellers from Europe, Australia and other countries disclose vital information for terrorism watch lists such as the number of passports they hold from different countries and whether they have used alternate names or aliases in the past.
"Many of the leading visa-waiver countries are seeing their citizens going to Syria to join [the Islamic State] or al-Qaeda affiliates in that country and potentially returning home with training and new skills," a senior Department of Homeland Security official told the Washington Post.
"We want to ensure that we know exactly who is coming and have the most information possible to make good decisions."
US officials estimate that over 15,000 foreign fighters have travelled to Syria to fight for jihadist groups with over 2,000 of those coming from European countries and Australia.
The new measures will expand the Electronic System for Travel Authorisation which was implemented in 2008. This system requires travellers to submit information online before receiving an authorisation code to travel to the US.