According to a forecast by public broadcaster ZDF on Sunday, the AfD won 33.2% of the vote in Thuringia state, far ahead of the conservatives' 23.6% - a share of the vote that could allow the party to block decisions requiring a two-thirds majority.

Appointing judges or senior security officials is among such decisions. The AfD is led in Thuringia by Bjoern Hoecke, the party's most radical and controversial figure.

In the neighbouring state of Saxony, forecasts show the conservatives, who have run the state since 1990, on 31.5%, just 1.1 percentage points ahead of the AfD.

Saxony's premier, Michael Kretschmer, blamed the far-right's strength on Social Democrat Chancellor Olaf Scholz's divided coalition in Berlin. "There is a huge lack of trust in politics and this must stop," he said.

With just a year to go until Germany's national election, the result is having a devastating impact on Chancellor Scholz's ruling coalition.

The anti-immigration AfD party has been boosted by a deadly knife attack at a festival in the western city of Solingen, allegedly carried out by an illegal Syrian citizen whom authorities failed to deport.

The left-wing populist coalition Sahra Wagenknecht (BSW), which like the AfD wants to reduce immigration and end arms supplies to Ukraine, came third in both states just eight months after its founding.

The BSW could thus play a key role in forming governments in both eastern German states, which lag economically behind western Germany more than three decades after unification.

Leader Sahra Wagenknecht said her BSW party hoped to form a state government with conservatives and other parties in Thuringia but would insist on a different approach to Ukraine.

A poor result for Mr Scholz's coalition could fuel further internal strife as all three parties seek to reassert their identities ahead of national elections next year.

"I am not against conservatives. I am not against BSW. I am against the normalization of fascism," said Bodo Ramelow, the state premier of Thuringia, whose left-wing party was defeated despite his popularity.

Huy Hoang (according to Reuters, DW)