Authorities have yet to determine the motives behind the attack, but with its growing popularity, the opposition AfD party has become a target of increasing criticism and attacks over its anti-immigration and other ultraconservative policies.
A far-right German politician was seriously injured in a "politically motivated" gang attack in the north of the country, police said on Tuesday.
Assailants wielding wooden bars beat unconscious a lawmaker for the far-right Alternative for Germany (AfD) party in the northern city of Bremen in what police described as a politically-motivated attack.
"This is the result of the ostracism and agitation AfD faces", he said, suggesting other parties were partly responsible for the attack because they had compared AfD to the Nazis.
Chancellor Angela Merkel's spokesman, Steffen Seibert, wrote on Twitter that "the brutal attack on lawmaker Frank Magnitz in Bremen must be strongly condemned". "Hopefully, the police will be able to quickly catch the perpetrators".
"Anyone who carries out such a crime must be punished".
Bremen, Germany's smallest state, holds a regional election on May 26, the same day as the European Parliament elections in which AfD hopes to make gains.
Last week an AfD office in the eastern town of Döbeln was damaged by an explosion. Three suspects were detained.
Bremen is not considered an AfD stronghold, unlike three states in Germany's ex-communist east that hold regional votes in September and October.
And last weekend in Lower Saxony, the home of a local AfD politician was targeted with graffiti and a party office was attacked with a paint bomb.
Party co-chiefs Alexander Gauland and Alice Weidel called the latest assault the "result of the incitement to hatred by politicians and media against us".
Frank Magnitz was brutally beaten, his party said.
Johannes Kahrs, an MP from the Social Democrats, junior partners in the ruling coalition, also said "violence is never acceptable" and that "extremism in any form is rubbish".
Green Party politician Cem Özdemir tweeted, "Even towards the AfD there is no justification for violence", He added, "Whoever fights hatred with hatred ultimately allows hatred to win".