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. The Iranian delegation has yet to show up.

State of play: A senior U.S. defense official said the U.S. military is still not seeing any Iranian military movements on the ground that reflect a potential “closing’ of the strait.