Protesters locked hands and sat in front of the entrance to a drilling position in the northeastern village of Pungesti.

They prevented a lorry from entering and displayed banners reading "No to fracking", a controversial extraction technique that consists of injecting water and chemicals deep into rock to release gas.

Chevron started drilling its first exploratory Romanian well in May despite fierce opposition from residents who fear it will damage the environment in an area dependent on agriculture.

"Shale gas exploitation can not be done if it affects the life of hundreds of thousands of people living in the areas given in concession", said Laurentiu Ciocirlan, the Greenpeace campaign coordinator.

Chevron insists that its operations respect security standards and says that a decision on possible full-scale exploitation is to be made only in three to five years.

Previous attempts to drill in Romania were suspended twice at the end of 2013 owing to demonstrations by shale gas opponents.

Chevron argues that shale gas could prove crucial for Europe's energy security, especially as a crisis deepens in neighbouring Ukraine, a key transit country for Russian natural gas supplies.