U.S. and Iranian negotiators have not yet made any agreements during high-stakes negotiations amid a fragile two-week truce.

The talks were taking place with the “mediation” of Pakistan, a state news agency reported, but the exact format was unclear.

Mr. Vance was traveling to Islamabad with President Trump’s special envoy, Steve Witkoff, and son-in-law, Jared Kushner. The ...