He was speaking at an anti-terrorism conference in Seville just days after the Paris terror attacks which killed 129 people and a bomb threat in Germany which led to the cancellation of a football match between Germany and Netherlands.
"The organisation currently holds records of some 5,800 suspected foreign terrorist fighters contributed by more than 50 countries," Juergen Stock said in an address.
"But with some estimates putting the number of foreign terrorist fighters at more than 25,000 clearly a significant gap still exists between the number of foreign terrorist fighters we have identified and those estimated to have reached conflict zones."
Stock said there had to be more information sharing between nations and improved access to the data they have for organisations like Interpol.
"Information is the lifeblood of police work... this information needs to be shared with Interpol," he said.
Law enforcement and counter terrorism officials from around the world have gathered in Seville for a three-day conference to address ways to fight Islamic State and other extremist groups.
"The so-called Islamic state has sent a clear signal that is bringing its fight to our doorsteps and to our capitals," said Stock.
"We need to send an equally strong message that we are united in our efforts to protect citizens and combat this threat," he added.
A 2015 UN report showed an increase in the number of foreign fighters from last year, with more than 25,000 foreign jihadists from more than 100 countries now involved in armed conflicts.
A large number of fighters were travelling from Tunisia, Morocco, France and Russia, but the report cited new flows of jihadists from the Maldives, Finland, Trinidad and Tobago, as well as from some countries in Sub-Saharan Africa.
Nearly 6,000 foreign jihadists on Interpol radar: chief
19 November 2015
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Interpol has identified only 5,800 foreign fighters of the roughly 25,000 believed to have joined jihadist groups in conflict zones like Syria and Iraq, the head of the global police body said Wednesday.
