Mogherini, who will be the EU next foreign policy chief, said the European Commission will present by Wednesday a package of new sanctions that will target Russia in four sectors, including defense and finance.
"I think sanctions are part of a political strategy," she said adding that the situation in Ukraine was "getting more and more dramatic."
"We need to respond in the strongest possible way," Mogherini said.
Mogherini was chosen the European Union's new foreign policy chief at the EU summit on Saturday. She will replace Catherine Ashton who is to step down in October.