Wars can be fought on many fronts, as few stones are typically left unturned when seeking ways to gain the upper hand.
What do you expect, this is war and everyone tend to use all he could within the reach of it capacity to win the war, so I don't think there's any rule or limitation to a certain extent either of the two parties can go.
One of the ways one can easily win a war like this is to:
1. Block the route of their entrance
2. Cut the means of ammunition supply
3. Block the means to the financial assets
4. Cut the means to their access to food and water supply.
War is a fight between life or death, win or loss, no one takes it likely with the other by all means. i just wish this menace end soon.