BERLIN (Reuters) - German police raided several apartments on Friday as part of an investigation into what they say may have been a reconnaissance operation at Stuttgart airport, but said they had found no evidence of an Islamist attack plot.

Two men without luggage were seen observing security checks at the airport on Dec. 12. A day later, a similar incident was reported at Charles de Gaulle airport in Paris, prosecutors said, which had prompted police to step up security at Stuttgart and other nearby airports.

The suspects had also taken a woman to the airport and were watching her make her way through the security checks, prosecutors said.

“The searches turned up no evidence of preparations for an Islamist-terrorist attack,” prosecutors and police said in a joint statement.

Police searched several apartments in western and southwestern Germany earlier on Friday.

They said that security at airports were to be gradually brought back down to normal levels.