(ANSA-AFP) - BERLIN, SEP 20 - Germany has asked the Polish government to clear up "serious" visa fraud allegations ahead of elections in Poland dominated by immigration issues, sources in Berlin said Wednesday. Polish media reports said a system for giving out Schengen visas to people from the Middle East and Africa in exchange for money was put in place through the Polish consulates and some external companies in the countries concerned. German Interior Minister Nancy Faeser had called her Polish counterpart and Warsaw's envoy to Berlin had been asked to appear at her ministry over the issue, officials said. During the talks, Berlin demanded that Warsaw provide "rapid and complete clarification" of the "serious" allegations. The authorities say the scheme may have involved several hundred Polish work visas, while the opposition says the real number could be around 250,000. Poland's secret service said last week that seven people had been detained in the scandal ahead of October 15 elections in which the governing party is running on an anti-immigration platform. (ANSA-AFP).