(CNN) -- The situation in Ukraine "has worsened considerably" European Commission President Jose Manuel Barroso said in a joint press conference with Ukrainian President Petro Poroshenko in Brussels, Belgium, on Saturday. "The opening of new fronts and use of regular Russian forces is not acceptable and represents a grave transgression," Barroso said. Speaking to Russia's President Vladimir Putin by phone Friday, he urged him to change course, Barroso said. "No one's interest is served by new wars on our continent. No one's interest is served by confrontation. This is simply not the way that responsible, proud nations should behave in the 21st century."