Italy's ISAB refinery, owned by Russia's second-largest oil producer Lukoil, is operating normally even if a series of "difficulties" has complicated things, a manager at the company said on Friday.

"The plant is working regularly at the moment," ISAB Deputy General Manager for Human Resources and External Relations Claudio Geraci told Reuters in a phone conversation.

Geraci said there were some commercial issues that were making things more problematic but said these were manageable for the time being.

His comments come as Russia's invasion of Ukraine prompts the U.S. and Europe to impose sweeping sanctions, affecting companies and global payments systems.

On Wednesday the European Union excluded seven Russian banks from the SWIFT messaging system, but stopped short of including those handling energy payments.

"There are complications that make the running of a refinery as big as ours much more complex," Geraci said, without giving details.

He said the government in Rome had not asked for any specific information as yet on the situation at the refinery.

ISAB is owned by Swiss-based trading and supply group Litasco SA which sells 89% of its output. Litasco is controlled by Lukoil.

On Thursday Lukoil, majority owned by its head Vagit Alekperov and his deputy Leonid Fedun, called for a fast resolution to Russia's invasion of Ukraine. ISAB, located on the island of Sicily, is Italy's biggest refinery in terms of capacity, accounting for around 22% of overall capacity, according to data from oil industry body Unem.

"The company summoned us ... and said production and salaries will not be affected," said CGIL trade union local representative Fiorenzo Amato.

In 2019, before the COVID-19 pandemic sapped energy demand, ISAB's output totaled 10.6 MMt, 13% of Italy's total.