MAINZ, Germany (Reuters) - The ranks of potential Islamist attackers are growing, posing a major challenge to German security, the head of the country's police said on Wednesday.
Holger Muench said that German police now know of about 750 people from Germany who had travelled to Syria and Iraq. About a third of them have returned, he said.
Speaking as security fears grow in Europe after last Friday's attacks in Paris killed at least 129 people, Muench said he saw two major challenges.
"First, the international quality of the phenomenon and the global network of Islamist perpetrators," Muench, president of the BKA federal police, told a security conference in Mainz.
"And secondly, the growing number of potential perpetrators in this area and the question how we are going to tackle this."
Muench said about a fifth of the 750 who had gone to Syria and Iraq were women who were now living in the two countries.
"The higher the number of people, the harder it is for police to keep in check potential perpetrators and prevent crimes," he said.
Europe has been rocked by last week's terrorist attacks in Paris, claimed by Islamic State. On Wednesday, French police raided a flat in Paris, surrounding a building where an Islamist militant suspected of masterminding the attacks was thought to be holed up.
On Tuesday, an international soccer match was called off in Germany and two Air France flights bound for Paris from the United States were diverted for several hours after bomb threats.
Muench said there was currently no evidence that militant groups were taking advantage of the massive inflow of refugees into Germany as a way to "bring in terrorists" into the country.