Chevron said Sunday it has restarted work on its first shale gas exploration well in Romania, a day after protests forced the US energy giant to suspend the operation.

Romanian police declared the area around the planned mine a "special security zone" and installed check-points on all roads leading to the nearby village of Pungesti after Saturday's protests.

"Chevron can confirm that it has resumed activities in Pungesti commune," in northeastern Romania, the company said in a statement Sunday.

Hundreds of people, mainly villagers from Pungesti, broke through wire mesh fences around Chevron's site on Saturday to protest against its plans to drill for shale gas, forcing it to suspend work for the second time.

Nonstop protests have been staged for more than six weeks in the rural Romanian village.

On Sunday, journalists were denied access to the area. Locals contacted by telephone said there was a police officer stationed in front of every house.

Residents oppose the highly controversial drilling technique used to extract shale gas known as "hydraulic fracturing" or "fracking".

Widely used in some US states such as Pennsylvania and North Dakota, it has been banned in France and Bulgaria because of the risks of water and air pollution.

A study this year by Duke University in the US state of North Carolina showed that fracking increases the risk of contaminated drinking water.

Across Romania, thousands have taken to the streets to protest against shale gas over the past three months.

Last Monday, Romanian riot police forcibly removed protesters from a makeshift camp next to Chevron's drilling site in Pungesti.

Greenpeace slammed the operation as "a serious abuse against the freedom of expression".

The camp installed on a private field with the owner's agreement was evacuated on Saturday and access to it is now forbidden because "illegal equipment was found there", police said.

iw/cc

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