Secretary of State Marco Rubio will lead a sizeable U.S. delegation to the Munich Security Conference starting on Friday, underscoring the importance of transatlantic relations despite a "crisis of trust," the head of the forum said.

Wolfgang Ischinger, the former diplomat who chairs the annual gathering of security experts and policymakers, said more than 50 members of the U.S. Congress were expected, including Democrat U.S. Representative Alexandria Ocasio-Cortez.

Fifteen prime ministers or heads of state from the European Union will also attend the conference, which German Chancellor Friedrich Merz will open on Friday and continues until Sunday, he said.

"At the moment, transatlantic relations are, in my view, in a considerable crisis of trust and credibility," Ischinger told a press conference on Monday in Berlin.

"That is why it is particularly gratifying that the American side is showing such strong interest in Munich."

At last year's conference, Vice President JD Vance accused European leaders of censoring free speech and failing to control immigration.

The comments by Vance, who also met Alternative for Germany party leader Alice Weidel, began a series of criticisms of Europe by members of President Donald Trump's administration that have unsettled Washington's European allies.

Rubio is expected to deliver a speech on Saturday. Asked whether he expected a similar attack from Rubio, Ischinger said he assumed Rubio would speak about U.S. foreign policy and "not about issues that do not directly fall within his portfolio."

One of the main themes of the conference will be Europe's ability in the future to assert itself more strongly through its own capabilities and to speak with one voice, Ischinger said.

Europe's response to Trump's designs on Greenland, an autonomous Danish territory, showed that it could do so if required. Trump has backed off tariff threats against Europe and ruled out taking Greenland by force.

"We have to move away from this patchwork of 27 dwarf states in Europe who think everyone can just carry on as before. That cannot be," he said.

Ukrainian President Volodymyr Zelenskyy is expected to lead the delegation from Ukraine, shortly before the fourth anniversary of Russia's invasion.

Since canceling its attendance in 2022, Russia has not asked to be invited back, Ischinger said.

He said the Palestinian foreign minister and Israeli officials would attend, and Venezuelan opposition leader Maria Corina Machado will make a virtual appearance.