Istanbul (CNN) -- Riot police gassed and hosed down hundreds of demonstrators with water cannons outside a courthouse where one of Turkey's most lengthy and contentious trials is approaching its conclusion.
Crowds of protesters began arriving early Monday at the Silivri Prison Complex, which houses the 13th Istanbul High Criminal Court. This judicial body has been hearing one of Turkey's most polarizing and high-profile court cases.
The trials have been going on for nearly four years. Prosecutors accuse hundreds of suspects of being part of a covert ultranationalist organization that wants to overthrow the government and sow unrest.
Police initially barricaded the courthouse yard. When demonstrators tried to break through the barricades, police teargassed them and hosed them down with pressurized water cannons. Protesters were shown on live Turkish television broadcasts hurling bottles and rocks at the security forces.
The clashes continued for hours under a heavy downpour.
Protestors chanted "Government resign," "We'll die but we won't go back" and "We want justice." The crowds also sang the Turkish national anthem while waving flags showing the face of Mustafa Kemal Ataturk, the founder of the Turkish Republic.
The demonstrators included many youth groups, members of the leftist Turkish Workers' Party, and parliamentarians from the main secular opposition party, the Republican People's Party, known as the CHP.
"What is going on inside is not a court case, it is a comedic farce," said Muharrem Ince, a parliamentarian from the CHP, speaking to the crowd gathered outside the courthouse.
The lead prosecutor in the case submitted his closing arguments last week. The defendants were expected to make their closing remarks starting on Monday, but Turkish state broadcaster TRT reported that the hearing was delayed until Thursday due to tensions.
More than 60 of the 267 suspects have been in detention -- in some cases for years -- as the court case has slowly proceeded. Among those detained are the former commander of the Turkish armed forces, retired Gen. Ilker Basbug, and two lawmakers from the CHP.
The trials are known as the Ergenekon trials, a reference to a mythical story about the origins of the Turkish people.
Critics call them a politically motivated witch hunt aimed at stifling opposition. Supporters of the process argue the once-dominant military has a half-century history of overthrowing at least four governments in Turkey and meddling in civilian political affairs.