The top diplomats of Turkey and Russia were set to meet on Thursday for the first time since Ankara shot down one of Moscow's warplanes, as dozens of foreign ministers gathered in Belgrade.
US Secretary of State John Kerry was also in the Serbian capital for the annual ministerial council of the Organisation for Security and Cooperation in Europe (OSCE), where he called on Russia to back the ceasefire in eastern Ukraine.
Following a meeting with Kerry, Russian Foreign Minister Sergei Lavrov was due to hold talks later Thursday with his Turkish counterpart Mevlut Cavusoglu, marking the two countries' first high-level face-to-face talks since Ankara's downing of the Russian plane on November 24.
The incident along Turkey's border with Syria has badly strained relations between Ankara and Moscow, and Russian President Vladimir Putin vowed Thursday never to forget it in a strongly-worded annual state of the nation address in Moscow.
"We will not forget this complicity with terrorists. We always considered and will always consider treachery to be the ultimate and lowest act. Let those in Turkey who shot our pilots in the back know this," Putin told lawmakers.
On Wednesday Lavrov said he was willing to meet Cavusoglu, who was "insisting" on holding talks on the sidelines of the council.
"We will not be evading this contact", Lavrov said. "We will hear what Mr Cavusoglu has to say. Perhaps there will be something new after what has already been said publicly."
After arriving in Belgrade, the Russian told reporters that it would be "sad not to hear anything new" from the Turkish side.
The ministerial council, the governing body of the OSCE, brings together 40 foreign ministers and other high-level diplomats in Belgrade before Serbia passes the chairmanship to Germany for 2016.
While the spotlight was largely on Russia-Turkey relations, the dominant topic at official group talks in Belgrade was the crisis in and around Ukraine.
Kerry renewed his call "to both Russia and the separatists it backs to fully implement the Minsk Agreements", referring to the peace plan that includes the withdrawal of foreign troops and returning control of the border to Ukraine.
"This is the time for concrete steps to avoid this disastrous and unnecessary conflict, and begin the process of rebuilding in Ukraine's east," Kerry added.
Lavrov agreed there was a need to overcome the Ukraine crisis based on the Minsk agreement, stressing the need for direct talks between Ukrainian parties.
"We are convinced that there are real prospects for a peaceful solution," he said.
Russia on Wednesday accused Turkish President Recep Tayyip Erdogan and his family of involvement in illegal oil trading with Islamic State jihadists, ratcheting up the heat in the bilateral dispute.
The Turkish strongman accused Moscow of "slander" and has rejected Russian President Vladimir Putin's demands to apologise over the plane incident, saying that Turkey was acting well within its rights to protect its border.