A fighter from the Shi’ite Kata’ib Imam Ali (Imam Ali Brigades) militia runs as they search a house after taking control of a village from ISIS.

Months after he returned from Syria, a 24-year-old German suspected of joining ISIS militants was arrested on Saturday, German federal prosecutors said in a statement.

According to the statement, the suspect allegedly arrived in Syria in October 2013 and was a member of the group until he returned home in November,

German officials estimate around 550 of their citizens have made their way to Syria and Iraq to fight alongside ISIS, according to Agence France-Presse.

The surge in foreign fighting in Syria and Iraq has raised Europe’s fears of attacks on home soil when the fighters return.

The German suspect is to go before a judge Sunday, but has not been accused of involvement in any attacks and prosecutors stressed there was no link with this week’s bloody assault on the Charlie Hebdo magazine offices in France.

Authorities said they had searched the man’s home in Dinslaken in northwestern Germany but didn’t elaborate.

Last week, anti-Islam rallies in Germany hit record numbers.

Protesters marched in several German cities on Monday against higher levels of immigration and what they see as the growing influence of Islam, in defiance of an appeal from Chancellor Angela Merkel to spurn rallies she views as racist.

The rallies, organized by a new grassroots movement known as PEGIDA, or Patriotic Europeans Against the Islamization of the West, have become an almost weekly event in the east German city of Dresden in recent months.

Some 18,000 people, the biggest number so far, turned out in Dresden on Monday but similar rallies in Berlin and the western city of Cologne were heavily outnumbered by counter-protesters who accuse PEGIDA of fanning racism and intolerance.

The PEGIDA protesters waved Germany’s black, red and gold flag and brandished posters bearing slogans such as “Against religious fanaticism and every kind of radicalism.”

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