German police on Tuesday arrested six Syrian refugees suspected of preparing a terror attack. Photo: AFP file 

FRANKFURT: German police on Tuesday arrested six Syrian refugees suspected of preparing a terror attack, prosecutors said.

The suspects, aged 20 to 28, were detained in dawn raids that saw some 500 police officers swoop on residences in the cities of Kassel, Essen, Hanover and Leipzig.

The men are accused of belonging to ?the foreign terrorist group?, Christian Hartwig, a spokesman for the Frankfurt prosecutor?s office, said in a statement.

?The accused are also suspected of preparing an attack on a public target in Germany using weapons or explosives,? Hartwig said.

The investigators believe the men had not yet finalised their attack plan, he added.

The suspects arrived in Germany between December 2014 and September 2015 at the height of Europe?s migrant crisis.

Prosecutors declined to give further details about the case, saying the inquiry was still ongoing.

German security forces have been on high alert to the threat of terrorist attacks, particularly after a truck rampage claimed by terrorist killed 12 people in Berlin last December.

Last month, police arrested a 19-year-old Syrian suspected of preparing a terrorist attack in the country using ?powerful explosives?.

Domestic security officials estimate there are some 10,000 radical terrorists in Germany, with roughly 1,600 among them suspected of being capable of violence.