In his remarks prior to his departure for Salzburg, Ratas stressed the need for internal security to strengthen the external border of the EU.

"Our security and the openness of our internal borders strongly depend on the strength of the external border of the EU," Ratas was quoted by spokespeople as saying. "For this, we need to modernise infrastructure, develop unified requirements for defending the border, and also strengthen the European Border and Coast Guard Agency."

On the subject of Brexit, the prime minister said that he finds it important that the 27 member states are unified, and that the border issue regarding Ireland and Northern Ireland is resolved.

EU leaders will begin the informal summit with discussions on migration on Wednesday night. They will discuss the latest developments, evaluate the accomplishments in decreasing the number of illegal immigrants, and discuss collaboration with third countries.

On Thursday, the heads of state and government of the EU will continue with the subject of internal security and a more thorough discussion on improving police and judicial cooperation, as well as strengthening border security and cyber resilience.

The leaders of the 27 EU member states and European Chief Negotiator for the United Kingdom Exiting the European Union Michel Barnier will discuss the progress of negotiations with the UK, as well as subsequent actions. They will focus on future relations with the UK, the final round of negotiations and the border issue regarding Ireland and Northern Ireland.

Ratas is scheduled to return to Estonia late Thursday night.