(Updates with quote, forecast, details)

LJUBLJANA, May 22 (Reuters) - Slovenia's largest fuel retailer Petrol on Friday posted a 20% jump in first-quarter profit despite a drop in sales because of the coronavirus crisis.

Petrol reported group net profit of 21.8 million euros ($23.8 million), against 18.2 million euros in the same period last year, even as sales dropped 15% to 916 million euros.

The company gave no direct explanation on profit rise but commenting on its figures it did say there had been "a positive effect ... arising from the value of the derivatives used to balance out petroleum-product price quotes." It also said the coronavirus crisis impact kicked in only in March.

However, Petrol expects to miss its 2020 forecast made in December, according to which it expected a net profit of 109.8 million euros this year on sales of 6.4 billion.

"The business plan for 2020 cannot be achieved due to the pandemic and the resulting economic crisis," Petrol said.

It added sales of oil products could fall 14%-17% this year after they fell by 18% to 742,900 tons in the first quarter.

"Measures to curb the epidemic, taken by countries in which Petrol operates, have caused a significant decline of economic activity and restricted movement, which has a very negative impact on the sales of Petrol group," it said.

Petrol operates 509 filling stations in Slovenia, Croatia, Bosnia, Serbia, Montenegro and Kosovo.

Slovenia has so far reported 1,468 coronavirus cases and 106 deaths. It imposed a general lockdown in the middle of March and has gradually started lifting it from April 20.

($1 = 0.9151 euros) (Reporting by Marja Novak; Editing by Edmund Blair and David Evans)