REUTERS - Germany's domestic intelligence agency (BfV) fears a growing number of women have gone to Iraq and Syria to fight alongside Islamic State militants, its chief said on Wednesday.

Hans-Georg Maassen, the head of the agency, told reporters in Berlin there had been a sharp increase in the number of young women under 25 leaving Germany to join the insurgents.

He said that about 100 of the 700 Germans in combat areas were women and about half of those women were under 25.

Similar trends showing more Western women joining Islamic State (also known as ISIS or ISIL) than earlier radical Islamist movements have been reported from other European countries with large Muslim minorities such as France and Britain.

"We've seen a rise in the number of women who fall for the increased appeal of the recruiting activities both on the Internet and through direct personal contacts," Maassen said, adding the number of sympathizers in Germany had grown to about 7,500. "The threat is becoming increasingly complex."

He said that about 100 people from Germany who joined the insurgents had been killed. He said there were indications that the numbers of those killed had increased considerably since the start of 2015. About one-third of those who left Germany have returned and more than 50 of those had combat experience.

Last September, Chancellor Angela Merkel had said about 400 Germans and hundreds of other Europeans had traveled to the region to join the fight alongside ISIS.