"We have serious doubts about a number of elements in the charter of the Board of Peace related to its scope, its governance and its compatibility with the UN Charter," the European Council president said after an EU leaders' summit in Brussels.

"We are ready to work together with the US on the implementation of the comprehensive Peace Plan for Gaza, with a Board of Peace carrying out its mission as a transitional administration".

The founding charter of Trump's body for resolving international conflicts has a $1 billion price tag for permanent membership.

Although originally meant to oversee Gaza's rebuilding, the board's charter does not seem to limit its role to the Palestinian territory and appears to want to rival the United Nations.

Spanish Prime Minister Pedro Sanchez told reporters after the summit that his country had "declined" the invitation to participate in the body.

Trump unveiled the new Board of Peace at the World Economic Forum in the Swiss ski resort of Davos Thursday, joined on stage by leaders and officials from 19 countries to sign its founding charter.

Key US allies including France and Britain have expressed doubts.

London expressed concerns about the inclusion of Russian President Vladimir Putin, whose forces are fighting in Ukraine after invading in 2022.

France said the charter as it currently stood was "incompatible" with its international commitments, especially its UN membership.