The shootout involved one militant linked to an underground leftist group, Istanbul Gov Muammer Guler said. He did not specify which group.

The militant has a large amount of ammunition, including booby traps, and that is why he has been able to hold off dozens of officers, Gov Guler said.

Television footage showed police units surrounding an apartment building in the Bostanci district of the city. Police were firing automatic weapons and tear gas canisters, and occasional blasts have rocked the neighborhood.

Police helicopters were hovering above the site where ambulances and fire trucks were standing by.

Gov Guler said police detained 10 suspects from leftist, Kurdish and radical Islamic groups in about 60 separate raids overnight. 'They were planning to stage sensational armed attacks soon,' Gov Guler said. We have seized lots of weapons, bombs and booby traps.'

The raids came days before May Day, when police are usually on alert for clashes with leftist militants.

Last week, Turkey declared May Day a public holiday, bowing to pressure from labour unions. But authorities refused to grant permission for festivities to be held at Istanbul's Taksim square.

The site is symbolic because dozens of people were killed there in 1977 when unknown gunmen opened fire, causing a stampede.

May Day was barred from being a public holiday in Turkey following a 1980 military coup, whose leaders regarded the festivities as an opportunity for leftist activism. -- AP