"We need optimistic scenario for EU27 future. But it requires realistic diagnosis of causes of Brexit & its consequences for Europe. We need to assure citizens that we're able to bring back stability, sense of security, effective protection," he said on his official Twitter account.
The participants of the summit will also discuss Europe's migrant crisis and the issue of protecting Schengen borders.
On June 23, the United Kingdom held a referendum to decide whether the it should leave or remain in the European Union. According to the final results, 51.9 percent of voters, or 17.4 million people, decided to support Brexit, while about 16.1 million opposed it.