"We are surprised and concerned about the recent signals sent to the Russian Federation, which provide overly an optimistic [sic] perspective," the two countries' foreign ministers said in a letter, Censor.NET reports citing AFP via Yahoo! News.
The warning reflects concerns in eastern Europe that the West may ease its pressure on the Kremlin over Ukraine and seek re-engagement with Moscow in return for help in war-torn Syria.
Referring to recent demands by EU leaders that the 28-member bloc should work closer with the Eurasian Economic Union promoted by Moscow, the ministers said stronger economic ties were not "today's question".
Instead, the ministers whose countries joined the EU in 2004 said "optimistic and encouraging signals" undermined talks aimed at overcoming Russia's opposition to a free trade accord between Ukraine and the EU.
In the letter to top EU officials, seen by AFP, Lithuania's Linas Linkevicius and his Polish counterpart Witold Waszczykowski added that deeper economic ties with Russia hinged on a set of conditions related to Ukraine.
These include, among others, compliance with the Minsk agreements on Ukraine, the re-establishment of Ukraine's territorial integrity and Russia's willingness to drop trade restrictions against the EU, they said.
The ministers also complained that while Russia does little to meet the conditions, the West barely mentions them in its calls for closer ties.
European Commission chief Jean-Claude Juncker proposed closer cooperation between the EU and the Russian-led union last month, while German Foreign Minister Frank-Walter Steinmeier also recently promoted cooperation with the bloc.
The EU is expected to roll over sanctions against Russia imposed over Moscow's interference in Ukraine for another six months later this week.