Ukraine will keep targeting Russian oil-refining facilities despite U.S. discontent with its campaign, according to President Volodymyr Zelenskyy, who warned that Kyiv’s forces may be forced to retreat "step by step” without more military aid from allies.

The drone attacks are in retaliation against Kremlin strikes on Ukraine’s energy grid and part of an effort to compel Moscow to stop them, The Washington Post’s David Ignatius wrote in a column, citing an interview with Zelenskyy done Thursday in Kyiv.

Ukrainian forces have attacked more than a dozen refineries inside Russia with explosive-laden drones over the past month, slashing fuel production. But the strikes irked Kyiv’s allies in U.S. who are concerned about rising domestic fuel prices in an election year, the Financial Times reported last week, citing people familiar with the issue.