US Vice President JD Vance has said Iran must make a "meaningful" cut in its nuclear enrichment capacity if the seven-month war between the two countries is to end. He spoke in an exclusive interview with Reuters.

Vance said any deal would require Iran to scale back its capacity, not just offer assurances of future cuts. "If you don't want a nuclear weapon, then why do you need 60 per cent enriched fuel?" he asked.

"We're not going to trade words for actions," Vance said. He added that Washington remains open to a peace agreement.

Vance, seen as the White House's lead negotiator, brokered a provisional peace deal in June that quickly fell apart. The war has jolted energy markets and become a political issue ahead of the November midterm elections.

Vance said Washington is unsure who makes decisions in Tehran now. Iran's Supreme Leader was killed in joint US-Israeli strikes at the start of the war, according to reports.

Iran's Foreign Ministry rejected the claim and pointed to mixed messaging from US officials instead.