WASHINGTON (AP) — Ukraine has used U.S weapons to strike inside Russia in recent days, according to a Western official familiar with the matter.

The weapons were used under recently approved guidance from President Joe Biden allowing American arms to be used to strike inside Russia for the limited purpose of defending Kharkiv, Ukraine’s second-largest city.

The official was not authorized to comment publicly on the sensitive matter and spoke on condition of anonymity.

Biden’s directive allows for U.S.-supplied weapons to be used to strike Russian forces that are attacking or preparing to attack. It does not change U.S. policy that directs Ukraine not to use American-provided ATACMS or long-range missiles and other munitions to strike offensively inside Russia, U.S. officials have said.

Ukrainian officials had stepped up calls on the U.S. to allow Kyiv’s forces to defend themselves against attacks originating from Russian territory. Kharkiv sits just 20 kilometers (12 miles) from the Russian border and has come under intensified Russian attack.

In advancing in the northeast Kharkiv region, Russian forces have exploited a lengthy delay in the replenishment of U.S. military aid. In addition, Western Europe’s inadequate military production has slowed crucial deliveries to the battlefield for Ukraine.