Szymanski's comments come amid suggestions that the EU may begin to ease its sanctions on Russia later this year, as reported by Reuters.
While diplomats in Brussels expect the 28-nation bloc to extend the sanctions, which were introduced over Moscow's role in the conflict in Ukraine and expire in July, they also say that intensifying high-level contacts with Russia two years after it annexed Crimea from Ukraine may signal a thaw.
Read alsoJuncker says Russia visit for talks, no letup in sanctions - mediaEuropean Commission President Jean-Claude Juncker's plans to meet President Vladimir Putin in June in Russia. Juncker wrote to Putin in November suggesting closer trade ties between the EU and the Russian-led Eurasian Economic Union.
Moscow may have also given EU states advocating sanctions relief more arguments by last week returning to Kyiv jailed Ukrainian military pilot Nadia Savchenko in a prisoner exchange welcomed by Western politicians.
"The sanctions on Russia were imposed not because of Nadia Savchenko's capture, but because of a much wider problem, linked to Russia's aggression on Ukraine," Szymanski said at the Reuters Eastern Europe Investment Summit in Warsaw, in comments authorized for release on Tuesday.
"We cannot afford to back down in this process, which has to last longer, and which may bring about a moderation of the Russian position. We would undermine this whole experiment, this attempt to influence Russia in this way."
"The European Union's authority... in the future depends on the successful influencing Russia through sanctions," Szymanski said.
A former Soviet satellite, Poland has been a vocal critic of Russia's actions in Ukraine, and has repeatedly called on NATO to station troops on its territory in response to what it sees as Moscow's renewed assertiveness in the region.
Germany and France, on the other hand, want dialogue to avoid a further worsening of ties with Moscow, Europe's main energy provider. Germany's foreign minister said on Tuesday it was "no secret" that some EU countries were skeptical about extending the sanctions.
