The ministry said an investigation was underway but did not elaborate on the details of the weapon, which military experts said likely was a powerful 1,100-pound bomb.

According to the officials, 31 tanks will arrive at Grafenwoehr Training Area in Germany at the end of May, and the troops will begin training a couple of weeks later.

The U.S. agreed in October to send the surface-to-air systems, which can target aircraft, cruise missiles and shorter-range ballistic missiles.

While official coverage of Vladimir Putin showed him in mostly formal settings, photographs issued by Volodymyr Zelensky’s office showed the Ukrainian president taking selfies with soldiers, eating cake with them and drinking out of paper cups.

The delivery of the Patriot air defense system promised by the U.S. was expected in Ukraine sometime after Easter, Ukrainian air force spokesperson Yuriy Ihnat said.