Security forces use water cannons to disperse protesters outside a courthouse in Silivri, where a hearing on people charged with attempting to overthrow Prime Minister Tayyip Erdogan's Islamist-rooted government is due to take place.

Silivri, Turkey - Turkish police fired water cannon, teargas and pepper spray on Monday as they clashed with thousands of activists protesting outside a court in support of 275 people accused of plotting to topple the government, forcing a delay in the hearing.

Defendants in the trial of the “Ergenekon” group, an alleged underground network of secular arch-nationalists, were expected to begin their final defences on Monday after prosecutors in March demanded life sentences for 64 of them.

Retired armed forces commander Ilker Basbug is among the defendants, including other military officers, politicians and academics, accused of attempting to stage a coup against Prime Minister Tayyip Erdogan's Islamist-rooted AK Party government.

Demonstrators outside the court at the high-security Silivri jail near Istanbul waved Turkish flags and banners of left-wing and nationalist groups as they fought to break through police barriers.

“We are Mustafa Kemal's (Ataturk) soldiers,” the crowd chanted, referring to modern Turkey's founder, who is a figurehead for Turkish secularists.

Police fired teargas, water cannon and pepper spray in an attempt to disperse the crowd. Strong winds blew the pepper spray into the court, affecting defendants, journalists and dozens of opposition lawmakers who were among the spectators.

Chief judge Hasan Huseyin Ozese declined to launch the hearing given the chaotic scenes. It was not clear when the session would begin.

The four-year-old trial has drawn accusations of political influence over the judiciary. The process of defendants making their final defences is expected to take at least another two months, before a verdict is announced.

Ergenekon is allegedly behind much of the political violence, extra-judicial killings and bomb attacks which have troubled Turkey in recent decades - embodying anti-democratic forces which Erdogan says he has fought to stamp out.

Critics see the case as a ploy to stifle opposition, part of a grand plan by the leader to tame the secularist establishment, including an army that intervened to topple governments four times in the second half of the 20th century.

Investigation of the alleged conspiracy, which surfaced in 2007 when police discovered a cache of weapons in Istanbul, was initially welcomed by a public eager to see an end to the “Deep State” - a shadowy network of militant secularists long believed to have been pulling the strings of power.

But dissenting voices have grown over the last four years, with the European Commission expressing concern about the handling of Ergenekon and other conspiracy trials.

Last September, a court in Silivri jailed more than 300 military officers in another trial for plotting to overthrow Erdogan's government.- Reuters