There are multiple reports that the US will join the war on Iran, joining Israel in targeting nuclear facilities.
Example from earlier:
Israeli media says the US could join the war against Iran tonight
CNN reporting the same. As is Kann news (Israeli media outlet).
As for what Iran will do in response:
Oil price support on Iran retaliation likely to include mines in the Strait of Hormuz
This article was written by Eamonn Sheridan at www.forexlive.com.