Europe needs to regain control of its borders, Germany's foreign minister was quoted on Saturday as saying, after reports that forged Syrian passports are in the hands of Islamic State militants.
More than a million refugees, many fleeing war and violence in the Middle East, have arrived in Germany this year. Since last month's Paris attacks, concern has grown that Islamist militants may enter undetected among the influx.
On Tuesday, German media quoted Bavaria's Interior Minister as saying that refugees with fake Syrian passports have disappeared in Germany and there are grounds for suspicion that they may have had contact with Islamic State militants.
Foreign Minister Frank-Walter Steinmeier warned against lumping refugees in the same category as suspected terrorists and said many militants came from Europe.
"However, irrespective of this, it is important that we have more control again over who is entering and leaving Europe," Steinmeier said in an interview with newspapers in the Funke Medien Group.
He added that a suggestion by the European Commission to expand the powers of the EU's Frontex border agency, and an EU agreement offering incentives to Turkey to help stem the flow of refugees, were important building blocks towards better frontier control.
Earlier this month, the European Union said it would nearly treble its spending on frontier defense and create a new 1,500-strong rapid reaction force under proposals to tackle the migration crisis.