(Recasts, adds further clashes, pvs DIYARBAKIR)

By Ferit Demir

TUNCELI, Turkey, April 8 (Reuters) - Thousands of Turkish troops backed by helicopters launched operations against Kurdish guerrillas in southeast Turkey which left 10 members of the security forces and seven rebels dead over the weekend.

Military officials said three soldiers were killed, while nine of their colleagues were injured on Sunday alone in violence across the provinces of Tunceli, Bingol, Bitlis and Sirnak, near the Iraqi border.

"The intensity of the clashes gradually increased today ... Thousands of troops are being deployed in operations which are widening across the region," one military official said.

He said the armed forces killed four militants from the separatist Kurdistan Workers Party (PKK) in a clash which broke out on Sunday evening in Tunceli's Hozat district. Observers said it was the bloodiest clash with PKK rebels this year.

Another PKK fighter died in a clash in Bitlis.

In separate fighting along the border between Tunceli and Bingol, the guerrillas killed three Turkish soldiers.

Landmines also caused a series of casualties over the weekend. Seven soldiers and one village guard were injured on Sunday as a result of mines laid by the guerrillas in the Bitlis and Sirnak regions.

The PKK launched its armed separatist insurgency in 1984, and more than 30,000 people have died in the conflict.

The intensity of the fighting eased after PKK leader Abdullah Ocalan was captured and imprisoned in 1999, but fighting has flared up again in the last couple of years.

Annually fighting generally picks up in the spring as PKK rebels cross the border from the northern Iraqi mountains, where thousands of the fighters are based.

Most of the rebels infiltrate Turkey through the mountainous border province of Sirnak.

Among other clashes over the weekend, an officer from the gendarmerie paramilitary police and a member of the village guard militia were killed in a firefight with the rebels on Kupeli mountain in Sirnak.

Two PKK rebels were killed in the clash and four soldiers were injured.

Further north in Bitlis province, a sergeant was killed when he stepped on a mine, the second such incident over the weekend.

On Saturday morning, two soldiers in a search operation in the Bitlis countryside were killed when one of them stepped on a mine believed to have been planted on the road by the rebels.

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