French President Emmanuel Macron and his US counterpart Donald Trump have found "major points of convergence" on subjects including trade, Iran's nuclear programme and the wildfires consuming large parts of the Amazon, a French presidency official said Saturday.

After an unscheduled two-hour lunch before the opening of the G7 summit in Biarritz, Macron "created the conditions for a good degree of convergence within the (G7) group, after obtaining clarifications from Donald Trump" on key issues, the official said.

Their talks covered areas of both "agreement and disagreement," the official told reporters on condition of anonymity.

Regarding the escalating tensions between Washington and Tehran, for example, "Donald Trump confirmed that he does not see a conflict, that he wanted a deal with Iran," the official said.

A landmark 2015 nuclear deal between Western powers and Iran has all but collapsed after Trump unilaterally withdrew US support last year, reimposing sanctions that have crippled Iran's economy.

French diplomats have raised the idea of US waivers on sanctions affecting Iranian oil exports to India and China, or a new credit line for Tehran.

On the trade front, where Trump has threatened retaliation over France's new levy on US tech giants who pay the bulk of their EU taxes in low-rate jurisdictions, Macron insisted that "there is no reason to spark a trade war over this," the official said.

Macron told Trump "there's no link to make with a digital tax, which is in the common interest of France, the US and all large economies," the official said.

The two leaders also found common ground on how to respond to the major fires across large swaths of the Amazon, after Macron accused Brazil's President Jair Bolsonaro of failing to do enough in the face of an "international crisis."

That drew a stinging rebuke from Bolsonaro, who denounced what he called a "colonialist mentality."

Macron assured Trump he had no intention of pursuing "an anti-Bolsonaro policy, but a helpful policy."

Trump himself seemed contented after the lunch, which came after a series of combative tweets that suggested he was in no mood to compromise with this G7 peers.

"So far so good. The weather is perfect. Everybody's getting along. I think we will accomplish a lot this weekend," Trump said on Twitter, praising his "special relationship" with Macron.