Bulgaria's economy minister, Traicho Traikov, has sent a letter to Lukoil Bulgaria, the local arm of Russia's giant Lukoil, to examine whether the company has sufficient fuel reserves to meet the country's demand, the Economy Ministry said in a statement on Sunday.

Earlier that day, Moscow imposed restrictions on exports of fuel products to fight fuel shortages in the local market. The ban is expected to be valid for at least a month.

Traikov has requested Lukoil Bulgaria to provide information about the volume of its crude oil and petroleum products reserves.

The company, however, said on Saturday that "Sunday is a non-working day and the response can be obtained from Monday onwards."

The letter is not the first claim made by Traikov to Lukoil Bulgaria. In late March, the minister requested the company to draft a definite scheme outlining fuel price formation on the Bulgarian market, a move that provoked furious reactions from the company.

Following the expiry of the memorandum between the government and Lukoil Bulgaria for a one-month freeze of petrol prices in late April, domestic fuel prices again started to increase.

Just on Thursday and Friday last week, retail fuel prices went up by nearly 5%, bringing the growth rate since the start of the year to 15%.

Referring to the letter sent by Traikov, Darik Radio quoted sources as saying that Russia's ban on fuel exports would not affect Bulgaria, since Lukoil Bulgaria delivers from Russia crude oil, whose exports have not been restricted.