BERLIN (AP) — Four attacks in a week – three of them carried out by asylum seekers – have left Germany on edge and Chancellor Angela Merkel’s policies of welcoming refugees under renewed criticism.

Anxiety over Germany’s ability to cope with last year’s flood of more than 1 million registered asylum seekers first surged following a series of sexual assaults and robberies in Cologne during New Year celebrations.

But in the last seven days, the violence has become even more deadly.

The unprecedented bloodshed began July 18, when a 17-year-old from Afghanistan wielding an ax attacked people on a train near Wuerzburg, wounding five people before he was shot to death by police. The Islamic State group claimed responsibility.

On Sunday, a 21-yearold Syrian used a machete to kill a 45-year-old Polish woman in the southern city of Reutlingen. Authorities said the assailant and victim knew each other from working in the same restaurant, and the incident was not related to terrorism.

Also Sunday, a 27-yearold Syrian who was denied asylum detonated a backpack of explosives and shrapnel at the entrance to an outdoor music festival in Ansbach, killing himself and wounding 15 people. The Islamic State group claimed responsibility, and German security officials said a video on the attacker’s phone shows him pledging allegiance to the extremists.

The deadliest attack came Friday night in Munich. The German-born, 18-yearold son of Iranian asylum seekers went on a shooting spree and killed nine people. The youth had obsessively researched mass shootings, and authorities said the attack does not appear to be linked to Islamic extremists.

Experts say the attacks are likely to inflame anti-foreigner sentiment in Germany, creating a challenge for Merkel’s government.