US-Iran negotiations in Pakistan ended without agreement on Sunday after a 21-hour session, with Vice President JD Vance saying the central obstacle remained Tehran’s refusal to give firm assurances that it would not pursue nuclear weapons.

Speaking in Islamabad after the talks, Vance said the outcome was “bad news for Iran” more than for the United States. He said the American side had engaged seriously, but had not obtained the commitment it regarded as essential on the nuclear question.

Vance said Washington required an unequivocal undertaking that Iran would neither seek a nuclear weapon nor retain the means to acquire one rapidly. He added that the US delegation believed it had put forward its strongest offer and would now wait to see whether Tehran responded.