A suspected German left-wing extremist accused of involvement in attacks on members of right-wing groups in Hungary has been remanded in custody in Germany, federal prosecutors said Friday.

The man, identified only as Simeon T., is suspected of involvement in two attacks in February last year during an annual right-wing gathering in Budapest, the federal prosecutor's office said in a statement.

The gathering, which draws far-right radicals from across Europe, marks the anniversary of Nazi forces attempting to break out of the Hungarian capital when it was besieged by Russia near the end of World War II.

The first attack took place outside a cafe. Left-wing extremists used batons and other weapons to beat up three people, who were left with bruises and broken bones.

Simeon T. allegedly spied on the victims and kept watch over the area during the attack.

In the second, he and other members of his group are accused of following two people on the street, spraying them in the face with an unknown substance and repeatedly punching them, prosecutors said.

One man fell to the ground after a blow to the head and the attackers continued to assault him as he lay unconscious on the ground, they said. The victim suffered facial and skull fractures.

Members of Simeon T.'s group "share a militant, left-wing extremist ideology that rejects the democratic rule of law," prosecutors said.

"The organisation has set itself the goal of using violence against members of the right-wing political spectrum."

He is accused of being a member of a criminal organisation and of two counts of bodily harm.

The suspect was first arrested in December in Berlin. But federal prosecutors, who investigate more serious crimes such as those that are politically motivated, have now taken over the case.

While right-wing radicalism is often seen as a greater threat in Germany, there have also been growing worries over far-left extremism in recent years.

Simeon T.'s group has been dubbed the "Hammer gang", and the group's reported ringleader is named as Lina E., a student from Leipzig.

Last year a court jailed Lina E. and three other far-left activists for several years over violent attacks on alleged far-right supporters.

Lina E. has become a symbol for activists, with the slogan "Free Lina" appearing regularly at left-wing rallies, according to German media.