Russian President Vladimir Putin has scheduled some tense meetings on the sidelines of a summit of the Supreme Eurasian Economic Council in Minsk.
Putin aide Yury Ushakov said Putin will meet with Belarusian President Alyaksandr Lukashenka to discuss a dispute over the Uralkaly potash company.
The Russian firm's general director, Vladislav Baumgertner, has been held in Minsk since August on abuse-of-office charges.
Putin will also meet with Ukrainian President Viktor Yanukovych, where the main topic on the agenda will be Ukraine's integration with the European Union.
Kyiv could sign an Association Agreement with the EU in November, but Moscow has been pushing Ukraine to join the Russia-led Eurasian Customs Union instead.
Putin said earlier this month that Moscow would have to take "protective measures" if Ukraine signs the agreement with the EU.
Based on reporting by ITAR-TASS and Interfax