The Home Secretary is poised to bring in new laws to tackle British extremists in the wake of the horrific killing of American journalist James Foley by a jihadist with an English accent.
Theresa May said Britain must introduce all the legal powers necessary to win the struggle against terror that is feared to last for decades.
Banning orders for extremist groups will be looked at again alongside powers to stop radical preachers.
Mrs May also underlined changes to the law that mean naturalised Britons who are fighting overseas can be stripped of their citizenship and excluded.
In an article for The Telegraph, she said: ” We will be engaged in this struggle for many years, probably decades. We must give ourselves all the legal powers we need to prevail.
“I am looking again at the case for new banning orders for extremist groups that fall short of the legal threshold for terrorist proscription, as well as for new civil powers to target extremists who seek to radicalise others.”
She added: ” People who insist on travelling to fight in Syria and Iraq will be investigated by the police and security services.
“For those who have dual nationality, I have the power to strip them of their citizenship and exclude them from the country.
” Following the recent Immigration Act, I can, in certain circumstances, remove citizenship from naturalised Britons who are fighting overseas and exclude them too.
“And while it is illegal for any country to make its citizens stateless, any British national who returns from Syria and Iraq faces prosecution here for participating in terrorist activities abroad.”
Since the coalition came to power in 2010 more than 150 people have been excluded from Britain for “unacceptable behaviour” , including foreign hate preachers.
Police have also secured the removal of 28,000 pieces of terrorist material from the Internet.
Mrs May said: “The cowardly murder this week of James Foley, a man who was working to highlight the suffering of the Syrian people to the world, has demonstrated once again the very deadly threat we face from terrorism at home and abroad.”
The Government has come under pressure to contemplate working with the Assad regime to tackle the militants operating in Syria and Iraq, with former head of the army Lord Dannatt suggesting there was a need to build bridges with the Syrian president.
But Foreign Secretary Philip Hammond said an alliance with the Assad regime would not be “practical, sensible or helpful”.
The UK Government has called for Assad to be removed as Syrian leader as a result of his actions during the country’s bloody civil war.
Asked if the UK would have to collaborate with the Assad regime, Mr Hammond told BBC Radio 4’s World at One: “No. We may very well find that we are fighting, on some occasions, the same people that he is but that doesn’t make us his ally.”