And if the U.S. wanted to re-enact a modern form of the old "Cash and Carry" plan they imposed on the U.K. before Pearl Harbor, then they were within their rights to do so as well as long as they obeyed UNCLOS.
The additional U.S. direct intervention on the side of Iraq (e.g. weapons, training) has been pretty conclusively demonstrated to have been stupid and unhelpful with regard to geopolitical stability in the Middle East (several times over, by now).
But in any event, if Iran had really wanted to blockade Kuwait then they should have declared war and blockaded Kuwait (it doesn't exactly have a wide coastline), instead of mining international waters. At least then they would have the moral high ground should the U.S. still have decided to intervene.
The entire operation (and several other operations close in time in the Persian Gulf) was the US administration choosing to directly intervene in support of Iraq in the war with Iran; the limited scope of the intervention was a matter of sell it, above all to US domestic audiences, as something other than the direct support for Iraq that it was.