Lukoil Neftochim, a Burgas-based oil refinery, will be slapped with a fine for contaminating the city's air with hydrogen sulfide, Environment Minister Ivelina Vasileva has said.

Vasileva has told the Bulgarian National Television the official announcement is to come from local authorities later on Friday.

Over the course of 24 hours, alarming rates of hydrogen sulfide concentration have been measured in the air of Burgas, with residents reportedly complaining of a pungent smell.

In the night of Thursday into Friday, the rate reached a value 36 times above the norm, which later fell sharply to three times above, local media report.

Lukoil Bulgaria officials earlier explained they were testing equipment.  

The fine of up to BGN 0.25 M (approximately EUR 0.125 M, the maximum possible under current legislation) comes after the same refinery caused an oil spill in June of last year, with nearly 30 tons of fuel flowing into nearby rivers and protected territories.

After being imposed a BGN 0.1 M fine, Lukoil then argued the incident had been caused by a theft attempt.