A Turkish court on Tuesday jailed 23 people, including a well-known publisher and an academic linked to the main pro-Kurdish party, pending trial on charges of links to separatist militants, state media reported.

They were charged as part of an investigation into links between activists and the outlawed Kurdistan Workers Party (PKK) militant group under which hundreds of people, including elected mayors, are already on trial.

Among those jailed was Ragip Zarakolu, a publisher who has faced repeated legal action in Turkey over controversial books he has published. Professor Busra Ersanli, who was a member of the pro-Kurdish Peace and Democracy Party's (BDP) constitutional commission, was also charged and sent to jail.

State broadcaster TRT said the 23, who were questioned by prosecutors for some 11 hours, were charged with membership of an armed terrorist group.

The investigation is focussed on an organisation called the Union of Kurdistan Communities (KCK), which the PKK established in 2005 with the aim of creating its own Kurdish political system, according to a 2009 indictment.

Those charged were among some 50 people taken into custody by police over the weekend in connection with the investigation. A further 23 suspects were still being questioned, while the others were released. About 100 people were jailed pending trial in the same investigation one month ago.

The latest arrests followed a surge in PKK violence in recent months which prompted Turkish military air and artillery strikes against the PKK's bases in northern Iraq.

More than 40,000 people have been killed in the conflict between the PKK and the state since the militants launched their armed insurgency in 1984. The United States, European Union and Turkey all designate the PKK as a terrorist group.

Some 150 politicians and activists are being tried in Diyarbakir where a large courtroom has been specially built. Similar trials are being held in other cities across Turkey.

The European Union, which Turkey is aiming to join, is closely watching the investigation.

(Writing by Daren Butler; Editing by Angus MacSwan)