European Commission President Jean-Claude Juncker said on Tuesday Europe would remain "a peace project" and "a project for the future," just hours ahead of a European Union (EU) summit.
He made the remarks while addressing a special plenary session of the European Parliament on the outcome of the British referendum.
He reiterated regret over but respect for the choice of British voters.
"I urge the government of the United Kingdom to clarify as quickly as possible the situation," he said, adding "not today, not tomorrow, but quickly."
He also stressed that there would be no "secret negotiations" and no "prior negotiations."
Tuesday's summit will be the first one after Britons' historic decision to leave the EU. Leaders of the EU countries is now gathering in Brussels to discuss the terms of the divorce, among other issues.
