Ukraine’s allies are increasingly concerned that desperation in the Kremlin over an unrelenting string of battlefield failures may lead Russia to escalate its war, possibly using a massive attack on a target like a dam or even a weapon of mass destruction.

For the moment, there’s no sign Moscow is actually making preparations for such a strike, even as it ratchets up the rhetoric, according to officials from NATO countries who spoke on condition of anonymity to discuss sensitive intelligence. U.S. and European defense ministers rejected allegations from Russian counterpart Sergei Shoigu in a rare round robin of phone calls Sunday alleging Kyiv is preparing to use a "dirty bomb.”

Instead, the view among Ukraine’s allies is that the Kremlin is trying to scare them with the talk of such "unthinkable” weapons — along with strikes on the country’s civilian power grid — into reducing their supplies of weapons and other support for Kyiv. So far, the intimidation campaign hasn’t worked.