According to Juncker, the "single market only" proposal was put forward by governments of some member states.

"But I don't want to comment on the others, although some would be clever enough to see which options are close to my heart, but I'm not going to kill off the debate, or stifle the debate," he added.

Unlike Juncker, European Parliament President Antonio Tajani, who sat along with Juncker at the press conference, said frankly that he prefered the "most ambitious" one.

"We believe in Europe, we believe in the future of Europe, we always prefer the most ambitious option," he said.

Tajani, however, added that "the proposals from the Commission involve listening first" and that "debates are open."

The white paper came weeks before British Prime Minister Theresa May is expected to activate the Article 50 clause in Britain's EU membership by the end of March.

Article 50 refers to the formal procedure by which an EU member state notifies the European Council that it intends to leave the block.

Leaders of EU member states are due to discuss the white paper at a summit next week in Brussels. They will meet again in Italy on March 25 to mark the 60th anniversary of the Treaties of Rome, which founded the predecessor of the EU.

This year is regarded as crunch time for the EU, as several member states are set to hold general elections and euroskeptic leaders have the upper hand in the Netherlands and France in the polls.