Home secretary Sajid Javid wants British jihadis fighting in Syria to leave the region, or face 10 years in jail.
Javid is set to use new powers that will make it illegal to either enter or remain in terror hotspots overseas.
Syria, where Daesh (Islamic State) is based, will become a "designated area" under the Counter-Terrorism and Border Security Act.
Javid said: "I’ve asked my officials to work closely with the police and intelligence agencies to urgently review the case for exercising this power in relation to Syria, with a particular focus on [the city of] Idlib and the north-east.
"So anyone who is in these areas without a legitimate reason should be on notice."
Under the new legislation, British nationals will be forced to leave the area within a month if they do not have a valid reason to be there.
Javid is expected to announce the new power during a speech in London. The home secretary will use the speech to highlight the UK's role in fighting terrorism.
“More than any other country on Earth, the UK has a coherent, connected approach to intelligence and security and when threats appear, the world still turns to the UK for leadership, support and action.”
According to reports, some 900 British citizens have left the country to join Isis over the past seven years. However, only 40 out of 400 jihadis have been prosecuted after returning home. More than 350 have been allowed to go free due to lack of evidence.
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