The United States has had no diplomatic relations with Iran following the hostage seize of the American embassy in Tehran that followed the 1979 Islamic Revolution.

US diplomats helped negotiate the landmark 2015 deal on Iran's nuclear programme with Europe under his predecessor Barack Obama but Trump unilaterally pulled out of the deal in May 2018.

Speaking after talks in northern France with French President Emmanuel Macron, an ardent supporter of diplomacy with Iran, Trump indicated he could consider talking to Tehran.

"I understand they want to talk and if they want to talk that's fine," said Trump, who is in northern France to mark the 75th anniversary of the D-Day landings.

"We'll talk but the one thing that they can't have is they can't have nuclear weapons," he added.

Trump said when he came to power Iran was "undisputed champions of terror" but indicated activity had slackened in recent times.

"They're not doing that anymore. They're doing very poorly as a nation. They're failing as a nation," said Trump.

Trump referred to the US sanctions against Iran which are battering the Iranian economy especially since Washington pulled out of the nuclear deal.

"I don't want them to fail as a nation. We can turn that around very quickly but the sanctions have been extraordinary."

Although EU leaders were bitterly angered by Trump's pullout from the nuclear deal, the US president said and Macron did not have differences on how to handle Iran.

Macron said the US shared the same four objectives on Iran -- to prevent it obtaining nuclear weapons, reduce its activities in ballistics, contain Iran's operations in the region and promote regional peace.

The French president said that in order to achieve such objectives "you need to start a negotiation" and applauded Trump's apparent readiness to hold talks.

"I think the words pronounced from President Trump today are very important," said Macron, speaking in English. "We need to open a new negotiation."

The comments came as Japanese Prime Minister Shinzo Abe, who has a warm personal relationship with Trump, plans to travel to Iran next week as Tokyo aims to play mediation role.

However Iran's supreme leader Ayatollah Ali Khamenei lashed out at Trump earlier this week, saying "when such a person is the president, this shows the political and moral decline of that country."