French President Emmanuel Macron, Italian President Sergio Mattarella, Belgium's Prime Minister Bart De Wever and Luxembourg's former grand duke Henri were among those in attendance.
The barrage came hours after Moscow rejected a plan by Kyiv and its Western allies to deploy peacekeeping forces to Ukraine should a ceasefire be reached.
A Russian warship arrived at South Africa's main naval base in Simon's Town on Friday to join Chinese and Iranian vessels in military exercises that risk further damaging Pretoria's relations with Washington.
The EU, he added, was "threatened from the outside by adversaries who are trying to unravel the bonds of solidarity that unite us" and "from within by democratic fatigue".