Europeans must not tire in their effort to defeat Russia's invasion of Ukraine, EU foreign policy chief Josep Borrell said Monday
He also warned that Vladimir Putin would seek to exploit "democratic fatigue".
Speaking after talks with EU foreign ministers, Borrell said the Russian leader "believes democracies are weak" and urged Europe to stand by its decisions to arm Ukraine and impose sanctions on Moscow.
"I'm sure Putin is counting on democratic fatigue," he said, responding to a question about fears that EU leaders resent the domestic economic cost of the sanctions and Russian disruption to energy supplies.
"EU member state governments have to continue standing behind the decisions they have taken. They took the decisions on restrictive measures on the Russian economy and they have to stick to it.
"For us this is a test of our resilience at the level of our societies. We have to be tough enough to hold on. We have no choice -- and neither do the Ukrainians."
Since February, when Russia invaded its already partially-occupied neighbour Ukraine, the EU has deployed an escalating series of sanctions packages against Moscow.
An oil import ban was decided in June and diplomats are now discussing a gold embargo, but many European countries remain dependent on Russian gas for their energy supplies.
Moscow, meanwhile, has exploited the dependence of some EU members on Russian supplies by delaying and disrupting gas shipments, contributing to damagingly high energy costs in the bloc.
Borrell and most western leaders insist the sanctions have damaged Russia's economy and will only get tighter if Putin fails to withdraw his forces from Ukraine.
But last week, Hungarian premier Viktor Orban -- the closest EU leader to the Kremlin -- slammed the measures, arguing that Europe had "shot itself in the lungs" by hurting energy supplies.
