LONDON (AFP) - British nationals spending time in Syria face arrest and up to 10 years in jail on their return home in new anti-terrorism legislation passed by Parliament.
Intelligence services estimate there are hundreds of British fighters still in Syria - with the territorial demise of the Islamic State bringing their fate into sharp focus.
The new British law, which received royal assent on Tuesday (Feb 12), toughens previous legislation that required the authorities to prove returning nationals had engaged in terrorist activities while abroad.
Interior minister Sajid Javid will now have the power to declare any zone outside Britain a "designated area" in order to "protect members of the public from a risk of terrorism".
Just visiting such zones will now constitute a crime, with exceptions for those with a "reasonable excuse for entering, or remaining in, the designated area".
They include people providing humanitarian aid, armed forces, United Nations staff, journalists and those attending funerals or visiting ill relatives.
Britons will have a month to leave the area after the power is enacted, which is likely to be within a few months.
The government believes around 900 British fighters travelled to Syria, 20 per cent of whom were thought killed and 40 per cent returning home.
Counter-terrorism police chief Neil Basu last month told Sky News that around 200 British militants were believed to be alive and in the region.
United States President Donald Trump's announcement in December that US troops would be withdrawing from Syria set off a countdown for governments whose citizens, having joined IS, were captured by the US-backed, Kurdish-led Syrian Democratic Forces (SDF).
British authorities had found it difficult to prosecute those coming back to Britain due to the challenges in securing evidence of them committing individual acts.
Mr Javid said the new legislation would make it easier to "punish those who seek to do us harm". The United States had said it is ready to help countries repatriate IS militants detained in Syria but that ultimately it is up to their home governments to come up with solutions.
"We call on all countries to step up and take responsibility for their citizens that went to Syria to fight for the Islamic State," a US State Department official told AFP, on condition of anonymity.