Iran and six world powers began expert-level talks on Monday to work out nitty-gritty details in implementing a landmark accord for Tehran to curb its disputed nuclear program in return for a limited easing of sanctions.
U.S. Secretary of State John Kerry postponed a trip to Israel scheduled for this week.
Two suicide bombings rocked Iran's embassy compound in Lebanon on Tuesday, killing at least 23 people including an Iranian cultural attaché and hurling bodies and burning wreckage across a debris-strewn street.
The New York Times reported on Saturday that the United States and Iran have agreed in principle to hold one-on-one negotiations on Iran's nuclear program but the White House quickly denied that any talks had been set.
Iran would enrich uranium up to 60 percent purity if negotiations with major powers over its nuclear program fail, an Iranian lawmaker said on Tuesday, in comments that may add to Western alarm about Iranian intentions.