Russia's largest private oil firm Lukoil said Friday its profits had fallen 58 percent year-on-year in the second quarter.

The company reported its net income was $1 billion between April and June, compared to $2.4 billion in the same period last year.

This figure was lower than experts had predicted, with Interfax news agency quoting analysts forecasting profits of $1.3 billion.

Lukoil said in a statement that its financial results had been affected by "a sharp decrease in hydrocarbon prices," as well as a "non-cash write-off" of $324 million.

The slide in oil prices and Western sanctions over Moscow's role in the Ukraine crisis have pummelled the Russian economy in recent months, leading the ruble to collapse.

Russia's recession deepened in the second quarter as gross domestic product contracted by 4.6 percent compared with the same period last year.

Lukoil's sales were also down more than 26 percent year-on-year, dropping to $28.1 billion.