Russia's energy minister said that oil is expected to resume flowing through a key pipeline to Europe by the middle of May, after contaminated supplies disrupted exports.
Aleksandr Novak also said on May 7 that four people had been arrested as part of an investigation into the contaminated oil, which caused major disruptions and tarnished Russia's reputation as a reliable supplier.
Russian news agencies quoted Novak as saying that the government had put in place stricter measures to prevent a repeat of the problems with the Druzhba pipeline, which first emerged on April 25.
"Investigations revealed a group of companies was carrying out illegal activity," Novak was quoted as saying.
He said some unnamed companies were allowed to introduce into the system oil that had excess chlorine compounds. The state-owned pipeline operator Transneft has accused a small private company of being responsible.
"The normalization of the situation" is expected in the first half of May, Novak said.
The Druzhba pipeline crosses from Russia into Belarus and then branches off. Some oil then heads toward Poland and Germany and some toward Ukraine, Hungary, Slovakia, and the Czech Republic.
Russian, Polish, Ukrainian, and Belarusian officials met in Minsk last month to discuss the issue.
Earlier, Russian President Vladimir Putin said that the contamination had caused “very serious” damage to his country's reputation as an oil exporter, and to Russia’s oil infrastructure.