The head of Interpol says countries need to improve their information sharing in order to effectively combat the threat of so-called foreign fighters.

Interpol's secretary-general Juergen Stock says an estimated 20,000 foreigners have joined extremists fighting in Syria and Iraq, including the Islamic State group.

About 3,400 foreign fighters are believed to have come from Europe, and authorities there are concerned about the threat they pose when returning home.

Stock told The Associated Press on Tuesday that rather than relaxing data protection laws countries simply need to take full advantage of existing rules to share information about suspects, money flows and weapons.

Speaking on the sidelines of an international police meeting in Berlin, Stock said Interpol plans to discuss the issue at a meeting with member states next month.