Russia’s production of crude oil shrank in August, lagging further behind its OPEC+ quota, after Ukraine stepped up attacks on the nation’s oil assets.

The country pumped an average of 8.718 million barrels a day of crude last month, the Organization of the Petroleum Exporting Countries said in its monthly report, citing secondary sources.

That was a drop of 160,000 barrels a day from a revised July average, and the biggest monthly decline since Russia’s output started shrinking in December.