They spoke at a nuclear energy summit which was briefly interrupted by Greenpeace protesters as the US-Israeli war with Iran entered its second week.

Von der Leyen said Europe's turn away from civilian nuclear power had exposed the continent's fossil fuel "vulnerability".

"It was a strategic mistake for Europe to turn its back on a reliable, affordable source of low-emission power," she said at the opening of the second Nuclear Energy Summit just outside Paris.

"For fossil fuels, we are completely dependent on expensive and volatile imports. They are putting us at a structural disadvantage to other regions," she said.

"The current Middle East crisis gives a stark reminder of the vulnerability it creates," she added.

"We have home-grown low-carbon energy sources: nuclear and renewables. And together, they can become the joint guarantors of independence, security of supply, and competitiveness -- if we get it right."

- 'Energy sovereignty' -

Macron said civilian nuclear power helped provide energy sovereignty.

"Nuclear power is key to reconciling both independence -- and thus energy sovereignty -- with decarbonisation, and thus carbon neutrality," Macron said.

"We can see it in our current geopolitical context: when we are too dependent on hydrocarbons, they can become a tool of pressure, or even of destabilisation," he added.

Von der Leyen said that "while in 1990, one-third of Europe's electricity came from nuclear, today it's only close to 15 percent".

"In the last years, we see a global revival of nuclear energy. And Europe wants to be part of it," she said.

She said European Union would "create a 200-million-euro ($230-million) guarantee to support investment in innovative nuclear technologies", unveiling a new strategy for small modular reactors.

"We want this new technology to be operational in Europe by the early 2030s."

Small modular reactors are advanced nuclear reactors that have a power capacity of up to 300 megawatts of electricity per unit, or about a third of the generating capacity of a traditional nuclear power reactor.

They are relatively simple to build, which makes them more affordable than large power reactors.

- 'Nuclear power fuels war' -

Nuclear energy fell into crisis after the 2011 Fukushima disaster in Japan, which reinforced fears highlighted by the 1986 Chernobyl catastrophe.

But the growing focus on energy sovereignty and the search for clean energies to counter global warming has reignited atomic interest.

The use of nuclear energy as an alternative to fossil fuels is highly controversial, however, with many environmental groups warning about safety risks and the disposal of nuclear waste.

The start of the summit was briefly interrupted by two Greenpeace activists who broke onto the stage as Macron greeted attendees and unfurled a banner reading "Nuclear power fuels Russia's war."

One of the activists shouted: "Why are we buying uranium from Russia?" before both were taken away by security personnel.

Greenpeace has accused France of maintaining ties with Russia's state nuclear corporation, Rosatom, despite Moscow's invasion of Ukraine, now in its fifth year.

In 2018, France's EDF signed a multi-million deal with a Rosatom subsidiary, Tenex, for reprocessed uranium from French nuclear power plants to be sent to Russia to be converted and then re-enriched before being reused in power production.

Greenpeace said that around 15 activists disrupted the arrival of officials heading to the event.

"This global summit on nuclear energy is completely out of touch with the current global situation, both in terms of geopolitical tensions and armed conflicts, and in the context of the fight against climate change," Greenpeace said.