The European Union's chief Charles Michel said the bloc should be ready to let new members from eastern Europe and the Balkans by 2030.
The Russian invasion of Ukraine has focused minds in Brussels on the need for new political momentum to support the European ambition of several membership candidates.
But, with fighting still raging in Ukraine and Moldova's pro-Western government scrambling to reform, senior officials have previously been reluctant to offer precise timetables.
"To be credible, I believe we must talk about timing and homework," Michel said, addressing the Bled Strategic Forum in Slovenia.
"As we prepare the EU's next strategic agenda, we must set ourselves a clear goal. I believe we must be ready, on both sides, by 2030 to enlarge.
"This is ambitious but necessary. It shows that we are serious."
Michel noted that the countries of the Western Balkans created out of the bloody break-up of Yugoslavia, began their quest to join the EU more than two decades ago.
Albania's Prime Minister Edi Rama welcomed Michel's announcement, calling for words to "materialize in... real steps forward," while voicing concerns that Ukraine's EU bid should not come at the expense of longer-standing candidates.
"Ukraine should be seen like a possible member state, but I wish this will not be (to the) detriment of the Western Balkans," he said.
Serbia's Prime Minister Ana Brnabic warned that waiting for a decade without negotiations since obtaining candidate status had fuelled euroscepticism in her country.
"We are geographically, economically, culturally, in every way European," she stressed, urging the bloc to "make that brave political decision" to integrate the Western Balkans into "the European family."
The president of the European Council endorsed the view of Germany's Chancellor Olaf Scholz that Europe should live up to the promises Brussels had made to candidate countries.
But he also backed French President Emmanuel Macron's argument that the union should also streamline its own decision-making processes before integrating new members.
