A Ukrainian drone attack on a natural gas processing plant in the Russian city of Orenburg has forced neighboring Kazakhstan to cut production at the Karachaganak oil and gas condensate field by 25 percent to 30 percent, two industry sources told Reuters on Monday.

One of the largest natural gas processing plants, Orenburg, was forced to stop receiving natural gas from Kazakhstan after the attack, Kazakhstan’s energy ministry said on Sunday.

Ukraine confirmed it hit the plant in the Orenburg region, located 1,700 kilometers east of Russia’s border with Ukraine, and a refinery in the Samara region.

Kiev has stepped up its attacks on Russian refineries and other energy facilities since August in an attempt to cut off fuel supplies and deprive Moscow of revenue it uses to finance the war.

Production at the Karachaganak field fell to between 25,000 metric tons (165,500 bpd) and 28,000 metric tons from the usual level of 35,000-35,500, according to two sources who spoke on condition of anonymity because of the sensitivity of the matter.

The sources said that Orenburg, which is controlled by gas producer Gazprom, will resume taking some quantities from Karachaganak today. They meanwhile refused to say when normal supply levels would be restored.

Oil and gas production at Karachaganak are closely linked, meaning the field is unable to produce much oil if gas production declines.

In addition to processing in Orenburg, Karachaganak gas is used for reinjection to maintain reservoir pressure, as well as for power generation at local facilities.

Karachaganak produced about 263,000 barrels of oil per day in 2004. This oil is exported by the Caspian Pipeline Consortium through a terminal on the Black Sea, as well as through the Russian Druzhba pipeline in Germany.

The field is managed by a consortium in which the American Chevron (18%) and the European energy companies Shell (29.25%) and Eni (29.25%) participate.

The Russian Lukoil participates with (13.5%) and the local company KazMunayGaz with (10%).

The consortium, Gazprom and Kazakhstan’s energy ministry did not respond to requests for comment.

Kazakh authorities agreed with Karachaganak shareholders in 2024 to build a new natural gas processing plant at the field with an annual production capacity of up to 4 billion cubic meters that is expected to start operating in 2028.

However, the project has been suspended under the current consortium and the government is looking for new investors, aiming to attract companies from Kazakhstan.

Industry sources said oil and gas condensate production at Karachaganak fell in September by 24% from August to 200,000 barrels per day amid maintenance work at the Orenburg plant.