Ukrainian President Petro Poroshenko and Russian President Vladmir Putin are among leaders gathering for a summit in Minsk on August 26.
The meeting comes amid heightened tension between Kyiv and Moscow over a pro-Russian insurgency in Ukraine’s east.
The summit of a Russian-led customs union will also be attended by Belarusian President Alyaksandr Lukashenka, President Nursultan Nazarbaev of Kazakhstan, and European Union officials.
Maja Kocijancic, a spokeswoman for EU foreign-policy chief Catherine Ashton, told RFE/RL in Brussels that the talks were "an opportunity for discussions on how to create conditions that would be conducive for the political solution for the crisis."
The Kremlin did not rule out Putin and Poroshenko holding direct talks, but would not confirm a bilateral meeting.
The two leaders last met briefly in France in early June at ceremonies to mark the 70th anniversary of the D-Day landings.
Russian Foreign Minister Sergei Lavrov said the meeting offers an opportunity for "an exchange of opinions about the state of the efforts to begin a political process aimed at resolving the crisis in Ukraine."
But Lavrov said EU representatives should not treat the talks as "a fight for Ukraine against Russia."
The EU and United States have imposed sanctions on Russia for its failure to rein in the separatists. Russia has hit back by banning most Western food imports.
On August 25, Poroshenko dissolved Ukraine’s parliament and announced snap elections for 26 October.
In a televised address, he said many current members of parliament were backers of ousted President Viktor Yanukovych.
He said a new parliament was needed to remove deputies who were blocking reform.
Meanwhile, the Ukrainian Security Service said its troops had captured 10 Russian paratroopers on Ukrainian soil.
It said the soldiers from the 98th airborne division were seized near the Ukrainian village of Dzerkalne, about 50 kilometers southeast of rebel-held city of Donetsk.
The Ukrainian military released a video purportedly showing some of the soldiers, who it said are being questioned as part of a criminal probe.
Earlier on August 25, Ukraine's army said Russian forces disguised as separatist fighters had crossed from Russia with ten tanks and two armored personnel carriers, and been heading toward the southeastern port of Mariupol.
The military said Ukrainian border guards engaged in combat against the column and stopped it outside Novoazovsk on the Azov Sea.
Kyiv has long accused Moscow of supporting the rebels in Ukraine.
Russia denies the allegation and says Ukraine's military campaign against the separatists is causing a humanitarian crisis.
U.S. national security adviser Susan Rice warned of a "significant escalation" in the conflict, saying on Twitter late on August 25: "Repeated Russian incursions into Ukraine unacceptable. Dangerous and inflammatory."
According to the United Nations, more than 2,000 people have been killed and about 340,000 forced to flee their homes in eastern Ukraine as a result of the conflict.
