A total of 13 defendants, most of them journalists, went on trial in Turkey Tuesday after being linked with a group allegedly attempting to overthrow the country's Islamic-based government.

The journalists included two well-known investigative reporters , who have been held in prison since March. The defendants are among hundreds of people, including journalists, academics and retired and serving senior military officers, who are already on trial in an investigation of the secularist network, Ergenekon.

Prosecutors say the group plotted in 2003 to bring down the government through bombings and other attacks to discredit the government and trigger a military coup against the ruling Justice and Development Party.

The trial highlights international concerns about press freedom in Turkey.

Foreign journalists traveled to Turkey to attend the trial. Those who could not get in demonstrated outside for their colleagues' release and unfurled a banner saying there can be no free society without free journalists.

Turkish authorities have detained more than 300 people as part of a wide-reaching investigation into Ergenekon.