Bulgarian lawmakers slapped on Wednesday a ban on shale gas exploration and production, bowing to strong public pressure over environmental concerns.

In a special resolution, the parliament "banned the use of the method of hydraulic fracturing for natural gas and oil exploration on Bulgarian territory and its Black Sea waters."

It also specifically banned "shale gas exploration using the above mentioned method."

Violators risked fines of 100 million leva (50 million euros, $65 million) and confiscation of all equipment, according to the resolution which was backed by 169 deputies of the 175 who cast votes.

Hydraulic fracturing or 'fracking' uses high pressure injections of water, sand and chemicals to blast through rock and release oil and gas trapped inside.

But although popular in the United States, opponents warn of the environmental impact, insisting there is high risk of contaminating the land and drinking water and of triggering earthquakes.

Wednesday's ban was a U-turn on previous government plans to start drilling for shale deposits in northeastern Bulgaria as a way to wean the country off its total dependence on Russian natural gas deliveries, and followed vehement protests from environmentalists across the country in recent months.

On Tuesday, the government revoked a five-year test drilling permit granted last year to US oil giant Chevron, citing "the lack of sufficient assurances that the commonly used shale gas drilling method of hydraulic fracturing can guarantee environmental safety."

Prime Minister Boyko Borisov meanwhile cited public pressure as the reason for backing off plans to develop shale gas, after anti-'fracking' rallies in Sofia and other major cities drew thousands of people last weekend.

Environmentalists welcomed the ban on Wednesday but insisted that shale gas exploration by 'fracking' should not only be banned in a resolution but forbidden by law, as is the case in France.

"A quickly adopted resolution can be cancelled just as quickly," Mariana Hristova from the Fracking Free Bulgaria group told AFP.