Forty seven Republican senators release a letter to Iranian leaders, saying any nuclear deal would require congressional approval.
Parties to the negotiations miss the self-imposed midnight March 31 deadline.
Iran and the major powers -- the United States, Britain, China, France, Germany and Russia -- agree to "key parameters" for a preliminary deal.
The White House relents when Congressional members demand lawmakers have a voice in the nuclear talks.
Iran and the major powers agree to give themselves until July 7 to reach a final deal.
Talks are once again extended, through July 10.
Negotiators missed U.S. congressional deadline, meaning the Republican-led U.S. Congress will now have 60 days, rather than 30, to review a deal. Iran and world powers extend talks again, to July 13.
Diplomats hint the two sides are close to having the complex document ready.