Scenario:

Let say that there has been a US intervention in Italy, and there is martial law.
There have been some act against US troops and order to confiscate firearms in the hands of civilian has been issued.

You are an US officer (let say 173rd Airborn Brg.) that suddenly meets a group of armed italian citizens that legally owns guns and the leader will speak to you like this:

"Sir, before your intervention we were law-abiding gun owners. Since the moment your troops and police aren't everywhere, we formed a militia and we need these guns to defend our families from bandits that want to kill us and loot our homes.
I've nothing against you or your govt. and we and this people didn't commit any act against US troops, it's easy for you to check that from this area attacks never started, and we have no intention to do anything in the future. But we are not going to surrender to you our guns and if you will try we are going to lead an armed reaction."

Would you try anyway to make them to confiscate their guns even by force?

Way too many assumptions in some ways and way too vague in others.  

My answer would be either yes or no depending on many other factors.

Say, "OK."

Leave.
Radio an airstrike on those cooridinates in 10 minutes.
No armed civilians to deal with.
Problem solved.

That's how I imagine it would happen to me, here, if I tried to argue with the Military.
Short of summary execution, that is.

No wonder why Iraqi shoots US troops.
If ANY army (mine included) would try to disarm me, I'd shoot first and then discuss...