A German state premier elected on Wednesday with the help of the far-right AfD says he is resigning to pave the way for fresh elections.

The election of liberal leader Thomas Kemmerich in the eastern state of Thuringia prompted national outrage.

“Resignation is unavoidable,” he said. For years Germany’s main parties have shunned Alternative for Germany (AfD).

Chancellor Angela Merkel – whose own party backed Mr Kemmerich in the vote – called the election “unforgivable”.

The AfD has grown in popularity in recent years but has been condemned for its extreme views on immigration, freedom of speech and the press.

Wednesday’s vote was described as a political earthquake as it was the first time the AfD helped form a government in Germany, breaking a consensus among the main parties to never work with extremist parties.

Mr Kemmerich has now announced fresh elections in the state, “to remove the stain of the AfD’s support for the office of the premiership”.

What happened in Thuringia?

Despite the AfD having broad support in Thuringia, the state election in October was won by the far-left Die Linke. And the liberal Free Democrats (FDP) had just 5% of the vote, barely scraping into the local parliament in the state capital, Erfurt.

But on Wednesday, in the secret vote to pick the leader of the government, Mr Kemmerich of the FDP beat Die Linke’s leader Bodo Ramelow by 45 votes to 44 – thanks to votes from the AfD.

Mr Kemmerich also got votes from local MPs in his FDP and Mrs Merkel’s Christian Democrats (CDU), prompting outrage from critics, who said the two centre-right parties had apparently made a pact with the far right.

Mr Kemmerich insisted there had been no co-operation with the far right and accused the AfD of carrying out a “perfidious trick to harm democracy”.

However, there are now suggestions the FDP and AfD had discussed a pact in Thuringia before.

A letter sent by AfD’s Thuringia leader to Mr Kemmerich on 1 November has gone viral on Twitter, in which the regional AfD leader offered his party’s support – either to form a technocratic government or a minority FDP-led government. It would break the long-standing red-red-green ruling coalition in Thuringia, he said.

The letter, first reported by regional broadcaster MDR at the time, shows that the AfD was seeking a deal long before Wednesday’s political shock.