KYIV, Oct 12 (Reuters) - The European Union will give a "firm answer" to a ruling by Poland"s top court challenging the primacy of EU law, and will tell Warsaw to "abide by the rules of the club," the EU"s top diplomat said on Tuesday. In comments to Reuters in the Ukrainian capital Kyiv, EU foreign policy chief Josep Borrell reiterated the executive European Commission"s concern about last week"s ruling, but did not indicate what steps it might take to bring Poland into line. Poland"s Constitutional Tribunal ruled that parts of EU law were incompatible with the country"s constitution, undermining the central tenet of European integration and fuelling talk that Poland could one day quit the 27-nation EU. Asked during a Ukraine-EU summit how the EU would respond to the Constitutional Tribunal"s ruling, Borrell said "the answer will be a firm answer". "It has to clear: You are a member of a club, you have to abide by the rules of the club. And the most important rule of the club is that the European law is over national law," he said. EU member states must accept the primacy of EU law as otherwise the bloc cannot "work as a union," Borrell said. The Constitutional Tribunal"s ruling followed prolonged disputes in which Poland has been accused by many of its fellow EU member states of curtailing the independence of media and courts under the nationalist Law and Justice (PiS) party. The European Commission is already withholding approval for Poland"s economic recovery plan, which Warsaw needs to tap into billions of euros to help revive growth after the COVID-19 pandemic. read more Despite growing tension, Polish Prime Minister Mateusz Morawiecki says Poland has no desire to leave the EU. read more GAS SUPPLIES At the Ukraine-EU summit Borrell was attending, EU leaders said the bloc would help Ukraine secure a steady supply of natural gas this winter and shield the country from any reduction in Russian output. read more Ukraine is lobbying its Western allies to punish Russia for what it says is Moscow"s attempt to use gas supplies as a weapon against Europe. Energy concerns also sparked a row between Ukraine and its EU neighbour Hungary last month, after Budapest signed a new long-term energy deal with Russia that sidelined Ukraine as a transit country. Ukraine wants the EU to investigate the deal, arguing it could violate EU energy rules. "Member states are free to do bilateral agreements," Borrell said. "As far as I know, there is nothing illegal, nothing that goes against European law, on this deal between Hungary and Gazprom."