[perennate]

I find your comment very misleading.

There is no indication that this arrest is related to U.S. policies to sanction foreign companies for selling to Iran.

Rather, the arrest is far more likely related to "US law [that] prohibits exports of certain US-origin technologies to certain countries" (from nytimes article). Huawei purchased certain technology from the US with the promise not to sell it to certain countries like Iran, and then proceeded to shamelessly violate the agreement.

Without laws like this, sanctions are far less powerful, because any foreign company not affected by the sanction can act as a middleman between the origin country and the sanctioned country.

What the UN International Court of Justice and European Union think about US sanctioning foreign companies that do business with Iran is completely irrelevant, since this arrest is not related to that policy.