MOSCOW: The quality of Russian oil flowing to northern and central Europe has deteriorated significantly in recent days, traders and Russian officials said, roiling the continent's refining industry.

Oil flows via the Baltic port of Ust Luga and via the Druzhba pipeline to Belarus, Poland, Germany, Hungary and the Czech Republic have been contaminated with high levels of organic chloride since April 19.

The material is used to help boost oil output but must be separated from oil before shipment as it can destroy refining equipment.

According to traders with several European majors, levels of organic chlorine have fluctuated at 150-330 parts per million (ppm) instead of the 10-ppm maximum norm and the usual level of around 1-3 ppm.

The Russian energy ministry confirmed there were quality issues and said pipeline monopoly Transneft was trying to fix the problem as soon as possible, giving no timeframe.

A Russian energy source familiar with the situation said the problem could be fixed by the end of the week.