>> The fourth act of violence to hit Germany in as many days, a 27-year-old Syrian man blowing himself up outside a crowded music festival in Ansbach on Sunday night. Twelve people were injured, three seriously. Bavarian police say it's unclear if the perpetrator, who acted alone, was an Islamist militant or not.
Reuters' Andrea Shalal is in Berlin.>> The mood in Germany right now is very difficult. There have been four separate attacks over the course of one week. They're not all related, and they're not all necessarily a sign of sort of some growing Islamist threat. But they do all raise questions about Angela Merkel's open door refugee policy.
People's nerves are frayed, people are anxious and nervous. We've had an attack on a shopping center, an attack on a train, now an attack on a music festival. Those are places that people have been going to, and want to continue going to. So everyone is very much on edge.
>> The Syrian man had been denied asylum in Germany a year ago and had twice tried to kill himself. It comes amid a string of attacks on German soil in the past week, prompting plans to strengthen the Bavarian police force and ensure they have adequate equipment.>> The security services in Germany have been constrained.
And there is some pressure from allies, other European countries, the United States, for the security services to do more. That's been extremely difficult in Germany because of privacy concerns that are very important in this country. It has a legacy of the East German Stasi, and of course World War II, the Gestapo.
>> More than a million refugees have entered Germany over the past year, many fleeing war in Afghanistan, Syria and Iraq. These incidents likely to make Chancellor Merkel's welcoming stance ever more unpopular.