I imagine that the severing of diplomatic relations would be a unilateral action that Denmark and Norway could take, but since the treaty is to apply even in the event of severed relations, it must be enforcable by the UN, regardless of the state of relations between the states involved.
Which means, I guess, that sanctions could theoretically be on the table... which would make the Bush administration soooooo happy. Sigh.
45. If diplomatic relations are broken off between two States, or if a mission is permanently or temporarily recalled: (a) the receiving State must, even in case of armed conflict, respect and protect the premises of the mission, together with its property and archives;
