Athens - Greek Prime Minister Antonis Samaras used the deadly Islamist attack on France's Charlie Hebdo magazine in an election campaign speech on Wednesday to slam the opposition Syriza party's proposals on immigration."Today in Paris, a massacre took place, with at least 12 dead. And here some people are encouraging even more illegal migration and promising naturalisation," Samaras, who leads the ruling conservative New Democracy party, told an audience in Halkida, around 100 km from Athens.The radical leftist party Syriza is narrowly leading the conservatives in polls ahead of the 25 January election.The party has caused alarm in other eurozone capitals by promising to ditch Greece's austerity course. Syriza also advocates a dramatic liberalisation of Greece's immigration strategy."Syriza is on another planet," said Samaras, accusing Alexis Tsipras's party of having a plan to naturalise migrants on a "massive" scale and give all illegal migrants access to social security and healthcare.In an earlier statement the prime minister had expressed "profound sadness and indignation" over the attack in Paris.There was no immediate reaction from the Syriza party.