Russia’s Defense Ministry said its forces were preparing a response to Ukraine’s recent attacks using U.S.-supplied ATACMS missiles on air defense units in the Kursk border region.

“In the last three days, the AFU carried out two strikes at objects in the Kursk region by long-range Western-made weaponry,” the ministry said in a statement on Telegram, referring to Ukraine’s armed forces. “Retaliatory measures are being prepared.”

Ukraine fired five of the U.S.-made long-range missiles on Saturday, targeting an S-400 battalion near Lotarevka, northwest of Kursk, Russia’s Defense Ministry said. Two of projectiles hit their targets, damaging a radar and resulting in casualties, according to the statement.

On Monday, Ukraine launched eight ATACMS missiles at the Kursk-Vostochny airfield, less than 10 kilometers (6 miles) east of the regional capital. Seven were shot down by air defenses while one hit its target, the ministry said.

Last week, Moscow’s forces launched an experimental intermediate-range ballistic missile known as Oreshnik at the Ukrainian city of Dnipro in retaliation for Kyiv’s first known use of western-supplied long-range weapons to strike Russian territory. President Vladimir Putin later said his forces may use the new missile in combat again.

The move came after a week of escalation that saw Putin lower the threshold for using Moscow’s nuclear arsenal and Joe Biden reverse course and allow Ukraine to use U.S.-supplied ATACMS missiles to strike Russia. Ukraine also launched U.K.-made Storm Shadow missiles against Russian targets.

The decisions by London and Washington to allow the strikes, which Kyiv had long requested, came in response to the Kremlin deploying North Korean troops to fight against Ukraine, according to officials from both governments.

Ukraine’s Air Force said earlier on Tuesday that Russia launched 188 Shahed drones overnight, the most in at least a year, as well as four Iskander-type ballistic missiles.

---------