European Council President Donald Tusk in France, August 31 2016 | Etienne Laurent/AFP via Getty Images Donald Tusk: No return to migration ‘chaos of 2015’ Council president says restoring control of external borders is top of Bratislava summit agenda.

President of the European Council Donald Tusk said Thursday that the upcoming EU leaders meeting in Bratislava will focus on migration and terrorism threat, not the divorce from Britain.

U.K. Prime Minister Theresa May has not been invited to the gathering in the Slovak capital on September 16.

"It is my deep conviction that our priority should be to take back full control in the field of internal security, and on our external borders," Tusk said in a statement published after meeting with Luxembourg Prime Minister Xavier Bettel.

"It is not an accident that this issue, together with migration, was at the forefront of the referendum campaign in the U.K.," Tusk also said.

He has talked to EU leaders ahead of the meeting of 27 to help set its priorities, he said, adding that the top one remains "irregular migration."

"Our aim must be clear: Never again should we allow the chaos of 2015 to repeat in Europe," he said.

"It is not our intention to talk about the U.K. in Bratislava or our negotiation strategy vis-à-vis the U.K.," he added.