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ANKARA (Reuters) - The jailed co-chairman of Turkey’s pro-Kurdish opposition party will step down, he said on Thursday, depriving the party of its most successful leader as it faces charges of supporting terrorism.

Selahattin Demirtas, who as co-chairman of the Peoples’ Democratic Party (HDP) since June 2014 took it into parliament for the first time, said he would not seek re-election at a party congress on Feb. 11.

HDP officials said Demirtas had decided to step down as his party membership may be at risk. Under Turkish law, someone convicted of terrorism cannot be a member of a political party.

“In order to continue our path with new excitement, and to improve the culture of carrying out political struggle for people and not positions, I will not run for the chairman post at our congress,” he said in a letter to the party.

A former human rights lawyer, Demirtas, 44, has been held in jail for more than a year on terrorism charges for which the prosecutor is seeking up to 142 years of imprisonment.

Demirtas, was detained with 11 other HDP lawmakers in November 2016 as part of an investigation into supporting terrorism and Abdullah Ocalan, the imprisoned leader of the outlawed Kurdistan Workers’ Party (PKK).

“Despite the government-based dirty propaganda and baseless, lawless and immoral accusations and attacks against us, we are neither separatist, nor terrorist,” Demirtas said in the letter.