Thirty-seven persons were killed here today in a bloody May Day riot in which rival leftist groups battled each other with guns and wooden clubs and police used machine guns, tear gas and armored cars to quell the fighting.
The riot climaxed two years of mounting political violence in Turkey in which so far more than 200 people have died.
It occurred four days before the official start of campigning for general elections June 5 and prompted fears of a bloody pre-election period.
The four-party conservative coalition cabinet of Suleyman Demirel met in emergency session in Ankara to discuss the violence.
The police action is likely to lead to a repetition of earlier leftist charges of police brutuality.
It is also likely to increase tension between Turkey's warring leftist and rightist factions, whose violent clashes had led to general elections' being moved forward four months in a bid to end the slayings.
The fighting started as the last of some 100,000 marchers crammed into Istanbul's main Taksim Square for a May Day rally organized by Turkey's second-largest labor movement, the Confederation of Progressive Labor Unions.
It was triggered witnesses said, by a burst of gunfire from an unidentified source aimed at a group of Maoist marchers entering the aquare.
The Maoists, who numbered about 2,000, returned the fire.
Rival groups of leftists armed with clubs ran toward the scene of the shooting. Fighting broke out in several places in the crowded square.
Steel-helmeted riot police used tear gas and water cannon in an unsuccessful attempt to restore order.
After a policeman was felled by a bullet, they moved in with armored cars and fired machine pistols into surging crowd.
Witnesses said a woman was crushed to death beneath the wheels of an armored car.
Several persons were trampled to death by the panic-striken crowd.
The dead included two police officers and five women.
More than 60 people were injured and more than a hundred arrested, police said.
In a statement to reporters, Interior Minister Selahattan Ozbek said police had the situation under control and there was no need for army intervention.
The May Day rally was only the second of its kind in traditionally conservative Turkey.
Marchers carrying portraits of Marx and Lenin and banners denouncing the Demirel government had been converging on Taksim Square throughout the afternoon.
"The rally was proceeding peacefull until the shooting began," said Istanbul Mayor Ahmet Isvan, who was among the May Day crowd.
An hour later, the square - dominated by a recently opened Intercontinental Hotel - was littered with bodies, trampled May Day banners and abandoned leftist leaflets.
Intermittent shooting continued for several hours in side streets leading to the square, and angry marchers set fire to several private cars.