Officials in Moscow claimed that Ukrainian drones attacked the Kremlin early on Wednesday morning, calling it an attempt on the life of Russian President Vladimir Putin. The Ukrainian capital of Kyiv is said to be preparing for an attack this spring, which may further escalate the war between the two nations. According to a statement released by the Russian president’s office, the Kremlin was allegedly hit by two Ukrainian drones that were shot down by Russian electronic air defense systems. The assistant to President Volodymyr Zelensky’s office, Mykhailo Podolyak, tweeted that Ukraine had nothing to do with the drone attack. “Ukraine only engages in defensive warfare and does not launch any attacks against Russian Federation targets. This does not resolve any military problems.”

Putin was reportedly working at his home outside of Moscow at the time of the incident, according to Kremlin spokesperson Dmitry Peskov. According to the Kremlin, it would take “retaliatory measures whenever and wherever it sees fit.” According to a New York Times story, Moscow Mayor Sergei Sobyanin has prohibited illegal drone flights. He said that the decision was made because unmanned drones might hinder their attempts to enforce the law.

The anticipated assault on Kyiv has allegedly already begun, according to Al Jazeera and the private Russian mercenary company Wagner, with soldiers reporting “heightened activity along the frontline.” Eight people were murdered earlier on Wednesday in a Russian strike on a supermarket in Kherson, which will now be under curfew from Friday through Monday out of concern for more Russian attacks.

The New York Times reports that while Ukraine has not claimed responsibility for the majority of recent drone attacks reported by Russian authorities, including some that occurred close to the Russia-Ukraine border, this attack would be the “most audacious attempted strike on Russian soil” since Moscow started its invasion last year.