The main suspect in the assassination of a German politician last year previously worked as a campaign volunteer for the nationalist Alternative for Germany party (AfD), it has emerged.

Stephan Ernst is being held on suspicion of killing of Walter Lübcke, a local politician from Angela Merkel’s Christian Democrat party (CDU) who was shot dead outside his home last June.

The 46-year-old Mr Ernst has a history of involvement with far-Right German groups, but this is the first time he has been linked to the AfD.

The party has rejected accusations from its political rivals that it fomented an atomsphere of extremism that contibuted to the killing.

An AfD spokesman confirmed Mr Ernst attended campaign events and helped put up party posters for a regional election in Hesse in 2018, but stressed that he was never a party member and did not apply to join.

Mr Ernst initially admitted killing Lübcke and told police it was in revenge for the politician's outspoken support for migrants.

He later retracted his confession and now claims he only went to Lübcke’s house to remonstrate with him over his political views. He says he was accompanied by a second man who fired the shot that killed Lübcke.