The French president, Emmanuel Macron, has said he will use this weekend’s G7 summit to attempt to de-escalate tensions between the US and Iran and seek to overhaul the global corporate tax code to make corporations like Google and Amazon pay more.

World leaders including the US president Donald Trump, Britain’s Boris Johnson, Germany’s Angela Merkel and Japan’s Shinzō Abe will meet in the French coastal resort of Biarritz this weekend at a tense moment for international relations clouded by transatlantic rifts over trade, Iran and the climate emergency.

Macron told reporters in Paris that he would meet Iranian officials ahead of the summit to make proposals to de-escalate tensions since Trump pulled the US out of Iran’s internationally brokered 2015 nuclear deal and reimposed sanctions on the Iranian economy.

“We have made proposals either for a softening of sanctions or a compensation mechanism to enable the Iranian people to live better,” the French president told reporters, without giving more details.

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Macron warned of “a profound crisis for democracy in Europe and elsewhere”, saying it was up to leaders to defend and reinvent multilateralism, rethink capitalism and redefine modern democracy and “not leave it to nationalists”. He said the climate emergency was one of citizens’ biggest fears around the world and part of the growing anger at capitalism came from unfair tax systems.

The French president said he would push ahead with plans to overhaul what he called the “crazy” system in which tech giants – such as Google, Amazon, Facebook and Apple – were able to book profits in low-tax countries, no matter where revenue came from. He said they enjoyed something akin to a “permanent tax haven status”.

Despite Trump’s firm opposition to increased tax on tech giants, Macron said: “The big digital players are not contributing to the common good. I don’t agree with this system, I don’t think it’s a good one, including for American workers.”

Macron will also change the summit format, scrapping the tradition of signing a joint final communiqué at the end. This is in part to avoid a repeat of the fiasco last year when Trump threw Canada’s G7 summit into disarray by leaving early, scotching the final declaration.

Macron said that as a former sherpa himself who had spent full nights racing to get such communiqués agreed, they were a waste of time which could be better spent developing strategy. Instead there would be what he called “useful”, informal conversations “behind closed doors” to bring leaders closer on key issues.

The G7 group includes the US, France, Britain, Japan, Germany, Italy and Canada, and the European Union also attends. This year Macron has also invited leaders from several other countries including India, Australia, South Africa, Senegal and Rwanda to widen the debate on inequality and climate change.

Macron said “finding a solution on Ukraine” on the basis of existing peace talks was an “essential precondition” for Moscow’s return to the group.

Russia was thrown out of what was the G8 in 2014 after it seized Ukraine’s Black Sea peninsula of Crimea, an annexation never recognised by the international community.

Asked whether he feared the US’s Trump and UK’s Johnson siding together against others at the G7, Macron said he did not think it was Johnson’s plan after leaving the EU for the UK to simply become the “junior partner” of the US, or a vassal state. He said the UK remained close to many European capitals on foreign policy.