Polish Prime Minister Mateusz Morawiecki called for the immediate release of Kremlin critic Alexei Navalny on Sunday after he was arrested on his return to Moscow, and urged the European Union to respond quickly."The detention of Navalny is another attempt to intimidate the democratic opposition in Russia. A swift and unequivocal response at the EU level is essential. Respect for citizens' rights is the cornerstone of democracy," Morawiecki wrote on Twitter."I appeal to the authorities in Russia to release the detainee immediately," he wrote.In September, Morawiecki suggested that Russia was a "hostile regime," after Germany said Navalny had been poisoned with a Soviet-style Novichok nerve agent.