The European Union and NATO called on the leaders of Kosovo and Serbia to attend crisis discussions without preconditions and prevent further escalation.
The EU's foreign affairs chief Josep Borrell has so far gotten no response to an invitation to Serbian President Aleksandar Vucic and Kosovo's premier Albin Kurti to meet in Brussels this week.
Brussels' mediation push comes as tensions have flared again over the detention of three Kosovo police officers by Serbia.
Vucic said on Sunday talks with Kurti were "pointless" until Serb demands are met, but he did not rule out attending.
Kurti said he was waiting for Kosovan representatives to get access to the detained police personnel before agreeing.
"The date of the meeting has not been set yet, because parties have not confirmed their attendance so far," said EU foreign affairs spokesperson Peter Stano.
"We expect them to show a reasonable attitude and to come to Brussels and to make the necessary efforts to de-escalate, and we take it from there depending on whether the meeting happens and how it goes."
Stano said the leaders were expected "to come without preconditions" and pointed to two upcoming meetings where EU states could discuss measures against the two sides if they don't cooperate.
NATO also called on all parties in Kosovo to stop any further escalatory steps and return immediately to the dialogue negotiated by the European Union.
"Our forces, the KFOR, will continue to take all necessary measures to ensure a safe and secure environment," NATO Secretary-General Jens Stoltenberg said after meeting German Chancellor Olaf Scholz in Berlin.
The detention of the police officers is the latest flare-up after weeks of tension between the two sides over disputed elections in Serb-majority northern Kosovo.
Rioting by ethnic Serbs in northern Kosovo saw 30 NATO peacekeepers injured in late May.
The EU had threatened Kosovo with political consequences such as suspending high-level visits and financial cooperation if it does not reverse course on the elections.
Tensions between Kosovo and Serbia have persisted since a war in the late 1990s that drew NATO intervention against Belgrade.
Kosovo declared independence from Serbia in 2008, but Belgrade has refused to recognize it.
Serbs in Kosovo remain largely loyal to Belgrade, especially in the north, where they make up a majority and reject every move by Pristina to consolidate its control over the region.
Serbia has long seen Kosovo as its spiritual and historical homeland, the scene of pivotal battles over the centuries. It continues to host some of the Serbian Orthodox Church's most revered monasteries.