A model of a pipeline is seen at the main entrance to the Gomel Transneft oil pumping station, which moves crude through the Druzhba pipeline westwards to Europe, near Mozyr some 300 km (185 miles) southeast of Minsk January 8, 2010. (REUTERS PHOTO)

MOSCOW, May 7 (Xinhua) -- Uncontaminated oil will start running again through the Druzhba pipeline to all the foreign consumers in the second half of May after a short suspension due to contamination, Russian Energy Minister Alexander Novak said Tuesday.

"As for the general normalization of the situation, we expect it in the second half of May. Work continues in this direction," Novak said at a government meeting, adding that normalization means clearing in each of the main export destinations.

On April 23, Belarus suspended the export of light oil products to Ukraine, Poland and the Baltic states after its state concern for oil and chemistry Belneftekhim reported a sharp deterioration in the quality of the Russian oil running through the Druzhba pipeline.

Currently, clean oil has resumed pumping through the pipeline to Belarus and Ukraine, Novak said.

The minister said that Russian investigation services had revealed a group of companies, which were using organochlorine compounds in an excessive amount in the oil to the Druzhba pipeline.

A source of oil contamination has been identified in the Lopatino metering unit in the Samara region in southwestern Russia, according to the minister.

"A criminal case was initiated... Four people were detained and placed in a detention facility by a court decision," Novak said.

Inspection documents have been transferred to the prosecutor's office, and Russia's Federal Security Service and the Investigative Committee are carrying out a set of operational measures and investigative actions, the minister added.