Germany’s domestic intelligence chief on Monday, Jan 12, urged Turkey to do more to prevent extremists crossing into Syria to join the Islamic State group and other terrorist organizations.

Authorities say that at least 550 people from Germany have traveled to Syria and Iraq to join extremist groups, along with more from several other European countries. Hans-Georg Maassen, the head of Germany’s domestic intelligence agency, said Turkey is a “key country” because well over 90 percent of the radicals traveled via the country.

While efforts to stop extremists crossing into Syria are partially successful, the number that have arrived remains too high — “so it is all the more necessary that the Turks take further measures,” Maassen told ARD television.

Turkey says the common-law wife of one of last week’s attackers in France arrived in Turkey on Jan 2 and crossed into Syria on Thursday, the day after the massacre at the satirical newspaper Charlie Hebdo.

Turkish Prime Minister Ahmet Davutoglu, speaking after meeting German Chancellor Angela Merkel in Berlin, later Monday rejected any suggestion that Turkey is doing too little against terrorism.

He pointed to the large number of foreigners who travel to Turkey, a popular tourist destination, and said that “we evaluate every tip that we get and our intelligence services work together.”

Turkey has issued entry bans against 7,000 people and sent between 1,500 and 2,000 back to their home countries, including people from France and Germany, he said.