* Nearly 100 members of the media in jail

* Government denies charges of media repression (Adds more quotes from defendants)

By Ece Toksabay

ISTANBUL, Jan 5 (Reuters) - Prominent Turkish journalists on trial for links to an underground anti-government network called the charges against them politically motivated and "a massacre of justice" in a case that has raised concerns over media freedom in Turkey.

Nedim Sener and Ahmet Sik, investigative journalists arrested in March and held since in a top-security prison outside Istanbul, were among 14 defendants in court to open their defence on Thursday.

Turkey is currently holding nearly 100 members of the news media in jail, one of the highest numbers worldwide, in a crackdown that critics and rights groups say blights Muslim Turkey's image as a role model for democracy in the Middle East.

"I am here because I am a journalist looking for the truth," said a defiant Sik, who has written books about the infiltration of the police by an Islamist movement led by Fethullah Gulen, a Muslim theologian based in the United States and considered close to parts of the ruling AK Party.

"A lie has been told from the start - that journalism was not put on trial here. The evidence against me includes 212 news stories, 247 phone tapping scripts and one book."

Sener, an award-winning journalist who has written about police negligence in failing to prevent the 2007 murder of prominent Turkish-Armenian journalist Hrant Dink, greeted observers as he entered a packed courtroom saying "Welcome to the theatre" and took a bow.

Looking thinner and with his voice trembling at times, he said the charges against him were baseless.

"I have put my life on the line by questioning Dink's murder. Our colleagues are in jail for writing news stories."

Sik and Sener are accused of belonging to 'Ergenekon', an ultra-nationalist group accused by prosecutors of being behind multiple conspiracies against Prime Minister Tayyip Erdogan's AK Party government.

If found guilty the two face a maximum of 15 years in prison. Both have denied the charges and say the evidence against them was planted.

Investigations into Ergenekon have spiralled since they first opened in 2007, and critics accuse the government of scaremongering to silence opponents. The government denies any such motives.

Several hundred suspects, including retired senior military officers, academics, lawyers and journalists have been detained in cases related to Ergenekon.

The other defendants in court on Thursday included Yalcin Kucuk, an author and television debate show presenter, and Soner Yalcin, editor of Oda TV, and several colleagues from the television website known for its criticism of the government.

Also in the dock was a former police chief, Hanefi Avci, who has written about the infiltration of the police by Gulenists.

The EU and the United States have raised their concerns over the arrests of journalists in Turkey. But with the economy growing rapidly and Turks tasting unprecedented prosperity and political stability, public outcry has so far been muted.

Turkey, a European Union candidate, is seen by some as a model of Muslim democracy in a region undergoing deep changes due to "Arab Spring" popular uprisings.

The AK Party is a socially conservative, economically liberal party led by pious Muslims. Secularists suspect the AK harbours a religious agenda, which Erdogan denies.

Critics says the crackdown on journalists is a reflection of Erdogan's intolerance and accuse the ruling AK, in power since 2002 and with a huge majority in parliament, of trying to silence critical media.

Government officials says the journalists are on trial for criminal activities, not because of what they wrote. (Writing by Ibon Villelabeitia; Editing by Rosalind Russell)

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