The Ministry of Environmental Protection refused to release data from a national soil contamination investigation launched in 2006, saying it involved national secrets, the Legal Daily reported on Monday.

The response was given in a letter on Sunday to Dong Zhengwei, a Beijing lawyer, who asked the ministry via an e-mail on Jan 31 to release information about the 2006 soil pollution investigation.

After the investigation, the ministry said it would release the results after an approval by the State Council, but Dong believes that the ministry didn't release the data because the pollution is severe.

Dong said the soil pollution data is important because it closely relates to the health and security of every citizen and that the ministry has no reason to refuse releasing it.

According to earlier reports, from 2006 to 2010, the Ministry of Environmental Protection and the Ministry of Land and Resources jointly held a national soil pollution investigation with about 1 billion yuan ($159 million) invested.

But the investigation results haven’t been released three years after it was finished.

On Jan 24, the State Council released a statement on soil pollution, saying that a soil-monitoring network will be built, covering 60 percent of the country's arable land and drinking water sources for more than 500,000 people.

It said that by 2020, the country's soil quality will be improved through effective protection measures.