BERLIN (Reuters) - Police raided sites in seven German states and detained two people in Berlin on Wednesday on suspicion of links to a gang smuggling Syrians through Poland to Germany, a federal police spokesman said.

The suspects are accused of fraudulently obtaining Polish tourist visas for Syrians so they could fly to Poland from the Gulf and then cross into Germany to apply for asylum, said spokesman Markus Pfau.

A third suspect could be detained later on Wednesday, he said.

Immigration remains a politically charged issue in Germany after Chancellor Angela Merkel’s decision to open the doors to more than one million migrants and refugees in 2015 and 2016.

Merkel has vowed to prevent a repeat of the unprecedented flows that overwhelmed Europe’s border controls at that time and numbers have fallen sharply, but Interior Minister Thomas de Maiziere said on Tuesday they were still too high. [nL1N1PB0K6]

Wednesday’s raids targeted 15 sites in Berlin and six other states as part of a joint German-Polish investigation launched in spring 2017.

The investigation, aided by Polish border authorities, found the gang was charging 8,000 euros ($9,778.40) per person to obtain a visa, and had earned a total of more than 300,000 euros ($366,690.00).

Germany’s de Maiziere said the successful raids showed the importance of border controls, adding that Poland had also taken additional measures. He did not elaborate.

About 48,000 asylum seekers from Syria arrived in Germany in 2017, according to data published on Tuesday, adding to almost half a million Syrian refugees who arrived in the previous two years.

The total number of asylum seekers registered in Germany in 2017 stood at 186,000, down 33 percent from 2016.