The prime ministers of Bulgaria, Greece, and Romania have expressed support for Serbia’s bid to join them in the European Union, saying the move would help guarantee regional peace and security.

“All of us know that the natural place of Serbia is in the European Union,” Bulgarian Prime Minister Boyko Borisov told reporters after a summit on October 3 in the Black Sea city of Varna.

Greek Prime Minister Alexis Tsipras, Romanian Prime Minister Mihai Tudose, and Serbian President Aleksandar Vucic also attended the talks, which focused on joint infrastructure projects, economic and energy cooperation, and security issues.

Borisov said the three Balkan members will work to speed the process of Serbia’s EU entry into the political and economic bloc, which currently has 28 members. Britain is in the process of exiting the EU, the so-called Brexit.

Serbia, along with Montenegro, is the Western Balkan country closest to joining the EU, having initiated accession talks with Brussels in 2014.

Serbian leader Vucic, a former nationalist, has remade himself as a pro-European Union reformer while at the same time seeking to maintain good relations with traditional ally Russia.

Despite the hopes of EU membership, Vucic on October 3 accused the bloc of having a double standard by refusing to accept this week’s Catalan independence referendum while having previously agreed to an independent Kosovo.

“We support Spain. It is our friendly country,” Vucic said. “But the European Commission responded in a different way [regarding Kosovo] and it was against my people and my state.”

Brussels has said Serbia must normalize relations with Pristina and end efforts to block Kosovo from joining international organizations. Belgrade has said it hopes to join the EU by 2019.