​Iran, U.S. at loggerheads as nuke talk deadline slips -- again

VIENNA -- In Tehran Friday, Iranian hardliners burned American flags at an annual rally against Israel. Secretary of State John Kerry's image was emblazoned on anti-America banners even as he continued to push for a nuclear deal in Vienna.

The deadline for an agreement over Iran's nuclear program has now been extended for the third time in two weeks. The deadline has been moved to Monday.

Neither side wants to be the first to walk away from a potentially historic deal. Still, Secretary Kerry claimed he would.

"If the tough decisions don't get made, we are absolutely prepared to call an end to this process," said Kerry.

It's been a week of rising tensions, including a shouting match between Kerry and Iran's top negotiator Javad Zarif.

Zarif accused the U.S. and its negotiating partners of bickering amongst themselves over lifting certain sanctions off Iran, one of the country's top demands.

In turn, the U.S. wants more limits on Iran's nuclear development now and even after a deal expires.

Kerry has devoted more time to this round of negotiations than any U.S. official in more than four decades. That's just one sign of how important closing this deal is to the Obama administration.

  • Margaret Brennan

    Principally assigned to the State Department, Margaret Brennan also serves as a CBS News general assignment correspondent based in Washington, D.C.