By Alexandra Hudson
BERLIN (Reuters) - Battle-hardened jihadists returning from Syria's civil war are no longer an 'abstract threat' but a 'deadly danger' to Europe, Interior Minister Thomas de Maiziere said on Wednesday.
An estimated 2,000 Europeans, including some 320 German citizens, have travelled to Syria to fight alongside Islamist rebels, he said while presenting the German domestic intelligence service's (BfV) annual report.
European governments are struggling to stop their nationals, some just teenagers, travelling to Syria where the conflict that began as a peaceful uprising to President Bashar al-Assad has become an armed rebellion is entering its fourth year. More than 160,000 people have been killed.
The trip to Syria is often as simple as a low-cost flight to Turkey then passage over the border with a trafficker.
"We had feared that those returning from the Syrian conflict might plan attacks here. We now know those fears were well founded. An abstract danger.... has turned into a concrete, deadly danger in Europe," de Maiziere said.
British Prime Minister David Cameron said on Tuesday that British and other European Islamists fighting in the Middle East posed the biggest threat to Britain's security.
BfV chief Hans-Georg Maassen said authorities had narrowly averted an Islamist attack in Bonn just before Christmas which would have harmed many people, and Germany remained a target.
The French citizen suspected of killing four people at a shooting at the Jewish Museum in Brussels last month spent time fighting in Syria and passed through Frankfurt airport, he said.
Germany has introduced anti-radicalisation programmes and hotlines for families worried their children might be planning to leave for Syria, but young people are still radicalising fast and often beyond the radar of intelligence services, he said.
The BfV report estimates there are some 43,000 Islamists in Germany, with the numbers of the ultra-conservative Salafi movement growing.
Maassen said the Internet played an important role in this recruitment process, evolving from a forum where extremists distributed information to a place where young jihadists were giving regular updates of their experiences via social media.
"Euphoric young people are sharing on the Internet what they are experiencing hour by hour," added the German security chief.
"They are posting gruesome pictures of executions, of severed heads... it is staggering to see the numbers of 'likes' and links, and it shows there is a group in Germany which is ready to be radicalised and to travel to Syria," he said.
(Editing by Stephen Brown and Tom Heneghan)