Tusk, the European Council President, called for an "honest and open debate" about the future of the EU, speaking at a summit of European People's Party Group in Luxembourg on Monday.

The group gathers various conservative factions from across the continent, with German Chancellor Angela Merkel and EU Commission chief Jean-Claude Juncker also in attendance.

In his speech, Tusk warned of the crisis facing the EU and slammed utopian "illusions" created by the bloc's politicians.

"It is us who today are responsible for confronting reality with all kinds of utopias - a utopia of Europe without nation states, a utopia of Europe without conflicting interests and ambitions, a utopia of Europe imposing its own values on the external world," said the former Polish prime minister.

Anti-EU forces cast themselves as an alternative to those illusions, according to Tusk.

"Obsessed with the idea of instant and total integration, we failed to notice that ordinary people, the citizens of Europe, do not share our Euro-enthusiasm. Disillusioned with the great visions of the future, they demand that we cope with the present reality better than we have been doing until now," he added.

Specter haunting Europe

His comments come less than a month ahead of a referendum in the UK, where the voters would decide on staying in the EU. Many observers fear that the so-called "Brexit" would lead to more countries opting out of the EU and the gradual disintegration of the 28-member bloc.

In recent years, eurosceptic forces have been gaining ground in many other states, including France, the Netherlands, Hungary and Tusk's native Poland.

Addressing fellow conservatives in Luxembourg, Tusk said that perfect European unity and integration might not be the best response to anti-EU forces.

"The specter of a break-up is haunting Europe," he said. "A vision of a federation doesn't seem to me like the best answer to it."