Ströbele, who has represented his Berlin electorate of Friedrichshain-Kreuzberg in Germany's parliament for four terms, announced late on Tuesday that he had decided to abstain next year.

"I will not be a candidate at the next federal elections, I have just told my Green base as much in Friedrichshain-Kreuzberg," Ströbele wrote on Twitter.

Ströbele told the German DPA news agency that he would see out his current term into next year, but with stressful 15-hour days when parliament was in session, he did not want to subject himself to a further four-year term.

He sat first in the Bundestag in 1985 as a list candidate for the Greens. In 2002, he won his Berlin seat outright for the first time, and has occupied it ever since.

Germany is due to vote in September 2017. Chancellor Angela Merkel told her CDU conservatives early last week the federal election campaign would be tough because of populist trends in Germany and across Europe.

Blocking Gauland

Ströbele aknowledged that the Greens had tried to persuade him to stay on so he could act as parliamentary elder to convene the next parliament. Staying would have blocked Alexander Gauland, 75, a deputy leader of the far-right Alternative for Germany (AfD) and ex-CDU functionary.

Born in 1939 and now 77, Ströbele was a leading left-wing lawyer during the student-led "extra-parliamentary opposition" of the 1960s and was a founder of Berlin's left-wing "Tageszeitung" (TAZ) newspaper.

Since 2014, Ströbele has been an outspoken member of the Bundestag's inquiry into the US National Security Agency (NSA) and has publicly sought asylum in Germany for the Moscow-exiled US whistleblower Edward Snowden, so he can testify.

Lammert also departing

Ströbele follows two other prominent federal parliamentarians, both members of Merkel's Christian Democrats (CDU), who recently said they would be ending their political careers.

Norbert Lammert, the parliamentary speaker, known as the "president" of the Bundestag, told his CDU electorate in Bochum in the Ruhr District in October that he would not seek re-election next year. The 67-year-old has spent four decades in politics.

Lammert, who has a reputation for robust rhetoric as well as wit, told Düsseldorf's "Rheinischer Post" (RP) newspaper last month that he turned down Merkel's request that he succeed Joachim Gauck as Federal President or ceremonial head of state.

"I simply didn't want it," Lammert told the RP. That refusal ultimately led to Merkel and her center-left coalition partners, the Social Democrats, agreeing on fielding a Social Democrat - Foreign Minister Frank-Walter Steinmeier - as a joint candidate for the next presidency. That post will be filled at a separate vote - via an electoral college - next February.

Binninger leaving

Also to bow out is the CDU's Clemens Binninger, 54, who chairs the Bundestag's oversight commission for Germany's intelligence services.

Binninger, a former police commissioner, told the "Stuttgarter Nachrichten" newspaper in September that he wanted to focus instead on family life with "another facet."

He has also been a leading CDU member at another federal parliamentary inquiry into ten murders by the NSU, a neo-Nazi ring exposed in 2011, and recently highlighted discrepancies in police sampling of DNA.

Communal politicians targeted

The three pending departures coincide with warnings from local politicians across Germany who have been subjected to hate speech online, often anonymously, mainly from xenophobes opposed to Merkel's liberal refugee policy.

On Tuesday, Thomas Purwin, 35, quit the chairmanship of the SPD's 500-member branch at Bocholt, near Münster in the western state of North Rhine-Westphalia (NRW).

Purwin, who also works in Bocholt's civil registry office, said a "boundary had been exceeded" by hate mail addressed to his daughter and his partner.

As a "family father" he could no longer tolerate months of intimidation, he said.

'Intimidation affects us all'

The SPD's Hannelore Kraft, state premier of NRW, Germany's most populous state of 18 million, said: "This intimidation affects us all."

Kraft said she was outraged that far-right rabble-rousers with their hate mail had brow beaten and worn down political representatives so much that "they had to terminate their work for democracy."

Last year, Markus Nierth, then the mayor of Tröglitz, a small town in Germany's eastern state of Saxony-Anhalt, quit his post, citing neo-Nazi intimidation of his family. Nierth faced the intimidation after speaking out against an apparent arson attack on a hostel that was readying to house asylum seekers. After quitting his political post, he continued campaigning on the refugee issue.

In July this year, prosecutors in Halle said they had terminated their probe, saying they had been unable to identify the perpetrators, despite interviewing 250 persons.

ipj/msh (dpa, epd, AFP)