The German government said Tuesday it has decided to postpone until after the summer break a parliamentary vote on a draft law on the controversial technology of "fracking" in Germany.

"We need to take time to clarify central issues. Thoroughness goes before speed," the environmental spokesman for the Social Democrat SPD party, Matthias Miersch, told German news agency DPA.

The Bundestag, or lower house of parliament, had been scheduled to vote on the proposed legislation -- which restricts hydraulic fracturing but does not ban it outright -- on Friday, the last day before the traditional summer break.

The cabinet had drawn up rules to ban fracking in specified regions "to protect drinking water, health and the environment."

Fracking or hydraulic fracturing is a process used to extract shale gas by blasting a high-pressure mixture of water, sand and chemicals deep underground to release hydrocarbons trapped between layers of rock.

Environmentalists argue that the process may contaminate ground water and even cause small earthquakes.

The technology is widely used in the United States, helping to keep down energy costs there. But it is banned in some countries in Europe.

In Germany, there have been no clear regulations in the past and the draft legislation aims to remedy that.

So far, fracking has never been used in Germany in shale, clay rock, marl and coal deposits at depths of less than 3,000 metres. That means not enough is known about its effects, particularly with regard to the water supply, drinking water and health.

In order to gather such knowledge, fracking is to be allowed for research purposes and only when the mixture of water, sand and chemicals do not endanger the water supply.