During a telephone conversation earlier in the day, Dmitry Medvedev and Viktor Yushchenko agreed to "continue discussions on topical issues in Russian-Ukrainian cooperation" at the forum in Russia's second city, the statement said.
The sides also discussed ongoing bilateral disagreements.
Medvedev urged his Ukrainian counterpart to avoid "unilateral steps contravening bilateral agreements," and "offered an objective assessment of a number of steps taken by the Ukrainian side that directly affect Russia's interests," the Kremlin said.
The Kremlin statement did not specify which disputes were referred to in the conversation.
Recent tensions between Russia and Ukraine have focused on Kiev's plans to join NATO, and the lease of a naval base in Ukraine's Crimea to Russia's Black Sea Fleet.
Former president Vladimir Putin warned in February that Russia could retarget its missiles at Ukraine if NATO bases are deployed in the country.
Frequent disputes have arisen over the lease of the Black Sea Fleet's base. Yushchenko recently ruled not to extend the lease beyond May 28, 2017. Earlier this month, Kiev barred Moscow Mayor Yury Luzhkov from Ukraine for saying the Crimean city of Sevastopol should be transferred back to Russia.
