The European Union's president, Herman Van Rompuy, has condemned the rise of extremist movements and populism as a threat to the free movement of people across the 27-nation bloc.
Van Rompuy, in a speech to Romania's parliament in Bucharest, said nationalist and extremist forces "are on the rise" and that this threatens further European integration.
His comments come after the candidate of the anti-immigrant National Front party won 18 percent of the vote in the first round of France's presidential election on April 22.
EU interior ministers on April 26 are due to discuss a French-German proposal to allow temporary border checks within the visa-free Schengen zone.
Romania and Bulgaria's admission into Schengen has been repeatedly delayed over claims they lack sufficient border protection against illegal immigration.
With reporting by AFP