In his first State Department news conference since breaking his leg last month in a bicycling accident, Mr. Kerry suggested major sanctions might be lifted long before international inspectors get definitive answers to their longstanding questions about Iranian experiments and nuclear design work that appeared aimed at developing a bomb. The sanctions block oil sales and financial transfers.

“We’re not fixated on Iran specifically accounting for what they did at one point in time or another,” said Mr. Kerry, who appeared by video from Boston. Instead, he said: “It’s critical to us to know that going forward, those activities have been stopped, and that we can account for that in a legitimate way. That clearly is one of the requirements in our judgment for what has to be achieved in order to have a legitimate agreement.”