US Vice President JD Vance said Washington and Tehran are close to agreeing a deal to extend their ceasefire in the Middle East war, but the potential breakthrough still hangs on President Donald Trump's approval.

Trump remained notably silent into Friday morning, despite US sources telling AFP a deal just needed his sign-off, underscoring the volatility of talks three months after the war rattled the Middle East and the global economy.

"It's hard to say exactly when or if the President is going to sign the MOU," Vance told reporters on Thursday. "We're going back and forth on a couple of language points. We've made a lot of progress here."

Optimism around a possible US-Iran deal boosted Asian stock markets on Friday, while oil prices receded slightly.

Energy markets have whipsawed this week as investors parse the chances of an agreement that could potentially resume normal shipping through the crucial Strait of Hormuz.