Extremism is contributing to and exploiting mass migration, the Home Secretary has warned.
Theresa May emphasised the need for international collaboration to tackle terrorism as she called on four of the UK's closest intelligence partners to work together in tackling the "challenge of our generation".
She also highlighted Britain's links with the UN and EU in counter-terrorism efforts.
Mrs May addressed representatives from Britain's partners in the Five Eyes security alliance - the US, Canada, Australia and New Zealand - in a speech in Washington.
She said: "I am clear that defeating terrorism requires a global response, and that we will not succeed by acting in isolation. This is the challenge of our generation.
"Extremism is spreading, threatening and taking lives, not just in our countries but in other lands. It thrives in the disorder created by fragile and failing states. It is contributing to, and in some cases exploiting, mass migration. It is turning the benefits of modern technology to its twisted ends."
The rise of Islamic State - also known as Isil, Daesh and Isis - has helped fuel a huge exodus from Syria as people flee territories seized by the murderous group.
Fears have also been raised that IS militants may have attempted to slip into Europe posing as refugees.
Last month a report by Europol said there was no "concrete evidence" that terrorist travellers are using the flow of refugees to enter unnoticed.
But it added that there are reports that refugee centres are being "specifically targeted" by Islamic extremist recruiters.
Mrs May called on Five Eyes partners to expand on "the successful co-operation between our countries on issues of national security which we have built over past decades".
She challenged the countries to:
:: Help vulnerable states improve their ability to respond to the threat from terrorism.
:: Stop messages of hate from spreading and prevent people from becoming radicalised.
:: Bring greater order and joint resolve to the "disparate work" taking place internationally and develop a comprehensive and coherent response to the common threat.
The Home Secretary insisted that the nations can no longer afford to see counter-terrorism work at home and overseas as "two separate entities".
She said: "If we are to deal with this threat effectively, we can no longer look simply to domestic solutions.
"There must be international co-operation, a common approach, free flows of intelligence and information, and the closing of technological gaps which the extremists exploit."
She referred to the unit for International Counter-Terrorism, a joint Home and Foreign Office centre which will drive the UK's work with the Five Eyes alliance and organisations such as the EU and the UN.
"Because it is no good arresting a person in your own country if they cannot be brought to justice in theirs," Mrs May said.
"It is no good ensuring world-class aviation security at home if people are not properly screened at airports abroad.
"It is no good sharing intelligence with another country if they cannot act on it effectively, and it is no good fighting terrorism in and from Syria if we can't help stabilise that country and its neighbours."
She also cited the European Union Internet Referral Unit, which was established last year to crack down on terrorist content on the internet and social media.
Mrs May said there is scope for more action "across the board", including better information-sharing, more active use of passenger data and more thorough exchange of terrorist finance information.