Trump 'not happy' with Iran but undecided on attack

US President Donald Trump has said he was frustrated by Iran's position in talks, but added he had not yet decided whether to carry out a threatened attack.

A day after the United States and Iran held talks in Geneva, Trump said on Friday that Tehran was "not willing to give us what we have to have."

"We haven't made a final decision," he told reporters when asked about the use of force.

"We're not exactly happy with the way they negotiated. They cannot have nuclear weapons, and we're not thrilled with the way they're negotiating," Trump said.

"We want no nuclear weapons by Iran, and they're not saying those golden words."

Iran has repeatedly denied it is seeking a nuclear weapon but insists it has the right to use nuclear technology for peaceful purposes, and US intelligence has found no evidence that it has decided to seek nukes.

Asked if an attack would trigger all-out war in the Middle East, Trump said, "I guess you could always say there's always a risk.”

"You know when there's war, there's a risk in anything, both good and bad."

The US president has claimed that Iranian authorities killed 32,000 people during a wave of protests that started in December and peaked on January 8 and 9.

Iranian officials acknowledge more than 3,000 deaths but say the violence was caused by "terrorist acts" fuelled by the United States and Israel.

Trump was circumspect on whether a US attack would bring down the Iranian government.

"Nobody knows. There might be, and there might not be," Trump said.

Trump, in his first term, ripped up a nuclear deal negotiated by his predecessor Barack Obama in which Iran agreed to strict limits on uranium enrichment.

Iran's Foreign Minister Abbas Araghchi earlier said that "success of talks requires seriousness and realism from the other side and avoidance of any miscalculation and excessive demands.”