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Erfurt Mayor Manfred Ruge said the attack was "like a slap in the face. I am deeply shocked."

The attack caused no injuries and the synagogue was spared extensive damage because the homemade bomb was badly designed, police said.

Wolfgang Nossen, a Jewish communal leader in the eastern state of Thuringia, criticized local politicians for not doing more to discourage right-wing extremism.

"Thuringia is a marching zone and a test ground for the neo-Nazis," he was quoted as saying. "While their demonstrations are forbidden in other states, they are allowed in Thuringia."

While welcoming the outpouring of support from the area's residents, Nossen said, "I would prefer that such shows of sympathy weren't necessary at all."

German police on Monday arrested an 18-year-old neo-Nazi suspected of carrying out the attack.

A member of the extremist National Democratic Party, the suspect denied involvement in the attempted arson during questioning by police.

Investigators believe the suspect did not act alone and are searching for accomplices.

A note found at the scene of the attack said, "This action is taking place on a purely anti-Semitic basis."

Police initially held 21 people after the attack, which took place after the group had been singing Nazi songs and shouting "Heil Hitler" in a bar not far from the synagogue. They were later released.

An increasing number of attacks have occurred on Jewish cemeteries in recent years. The last attack on a synagogue took place in Lubeck in 1995.

Meanwhile, several other incidents have been linked to neo-Nazi celebrations of Hitler's April 20 birthday.

Police arrested people singing right-wing extremist songs and hoisting Nazi flags in several cities. Police also reported increased neo-Nazi activity in the former East Germany, where right-wing extremism and neo-Nazism have been on the rise since Germany reunified 10 years ago.