Federica Mogherini met with the presidents of Serbia and Kosovo as part of an EU-mediated dialogue that is designed to solve their decades-long dispute, which has threatened the stability of the Balkans.
Kosovo declared independence from Serbia in 2008, but Belgrade does not recognize the move. Tensions recently have increased, with the two sides accusing each other of undermining efforts at reconciliation following a 1998-99 war.
Mogherini urged Serbia and Kosovo at the meeting to "refrain from words, actions and measures that are contrary to the spirit of normalization," a statement issued after the meeting said, adding "they discussed the necessary steps for the way forward."
It was not immediately clear when the next round of talks could be held.
Serbia's President Aleksandar Vucic complained in an interview with the state Serbian TV that Kosovo must first revoke tariffs it has imposed on good from Serbia and Bosnia, arguing they are in violation of a regional trade agreement.
Vucic also criticized Kosovo's plans to create and army, warning against any attempts to deploy the future military in Serb-dominated northern Kosovo where Serbia retains strong influence.
"We are always ready to talk ... but with those who cheat every day," Vucic said.
Kosovo's President Hashim Thaci described Serbia's attitude in the talks as "aggressive and arrogant."
"If Belgrade thinks it will be easy with the Kosovar side, it is wrong," he said. "I know it will be very difficult, it (dialogue) has a very little possibility for agreement but we should work upon that."
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