An agreement with Iran has not been reached because the country has refused to agree to a number of US demands, said JD Vance in a speech to the conservative organization Turning Point USA.
He said he will now "fight" to reach an agreement.
"We will continue to negotiate and try to make it a reality," Vance said.
Last week, delegations from the US and Iran were in Pakistan for peace talks in the capital Islamabad. However, JD Vance left the negotiations after less than a day, without any agreement being reached.
Since then, several messages have been exchanged through Pakistan, the Iranian Foreign Ministry said. On Wednesday, a Pakistani delegation arrived in the Iranian capital Tehran for new meetings, according to Iranian state media.
Vance did not specify when or how any new talks would take place. However, US President Donald Trump has recently hinted that a second round of negotiations in Pakistan could be underway in the near future.
On Tuesday, Trump told a journalist from The New York Post that she should stay in Pakistan's capital, Islamabad, for two more days.
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