ANKARA (Reuters) - The jailed co-chairman of Turkey's pro-Kurdish Peoples' Democratic Party (HDP) refused to attend a court hearing in the capital Ankara on Friday because police told him he would have to be handcuffed, his party said.

Selahattin Demirtas, held at a prison in the northwestern province of Edirne, had asked to be present at the hearing but then refused to travel to Ankara in handcuffs, it said.

"(Demirtas) stated he was still a lawmaker, that his immunity was still intact, and that he would not attend the hearing if he were put in handcuffs," a party statement said.

It said the prison gendarme told Demirtas they could not take him to Ankara without handcuffs, upon which he returned to his room at the prison.

HDP lawyers left the courtroom in Ankara in protest, a Reuters reporter said, while the public inside the court applauded the decision to handcuff Demirtas. Police dispersed a crowd outside the court.

More than a dozen HDP lawmakers, including the party's former co-leader Figen Yuksekdag, have been jailed, mostly due to suspected links with the outlawed Kurdistan Workers' Party (PKK), following an abortive putsch last July.

"This is an act of civilian coup, Selahattin Demirtas is the chairman of HDP and a lawmaker," Serpil Kemalbay, who replaced Yuksekdag after her arrest, told reporters. "It is just another dimension of the ongoing injustice, and totally unacceptable".

"We are protesting this use of force against our chairman and call for freedom and justice for all".

Prosecutors want Demirtas jailed for 142 years and Yuksekdag for up to 83 years on charges of terrorist propaganda. Demirtas was sentenced in February for "insulting the Turkish people, the government and state institutions".

The HDP also says as many as 5,000 of its members have been detained as part of a crackdown that followed last year's failed coup, and which rights groups say targets dissent.

The arrests handicapped the second-largest opposition party before an April 16 referendum in which Turks narrowly approved constitutional changes sharply boosting President Tayyip Erdogan's powers.

The government says the HDP is an extension of the PKK, which has waged an insurgency in Turkey's largely Kurdish southeast for more than three decades.

The HDP denies direct links to the PKK, deemed a terrorist organization by Turkey, the United States and European Union.

(Additional reporting by Gulsen Solaker; Writing by Tuvan Gumrukcu; editing by Ralph Boulton)