This is a quite new development. It cannot necessarily be called a military target such as air defences or supplies. It blocks the Danube.
It is an isolated event.
My guess is that it is a threat to the Serbian government to attack the economic infrastructure of Serbia on a massive scale, and that this threat has been conveyed to them through a diplomatic route.
On the one hand it appears strong, from another it is probably a sign that NATO admits that it cannot stop Kosovo been largely cleared unless it makes much more direct threats amounting to total war against Serbia.
Chris Burford
London