MUNICH (Reuters) - No government can guarantee its citizens full security from terror strikes, Germany’s president said on Sunday, calling for national unity as the best defense after attacks in the past two weeks left 15 people dead.

Slideshow ( 6 images )

“Nowhere on earth are there politicians who can make such a guarantee,” Joachim Gauck, a former Christian pastor in communist East Germany, told a memorial ceremony for the attack victims in Munich.

“What we can do, however, is something we need to work on again - that is the alliance of government bodies and an alert and active civil society. This is the best possible cover against the rise of the cynical calculus of violent attackers.”

Five separate attacks between July 18 and July 26, two of them claimed by Islamic State, also left dozens wounded and have burst any illusions in Germany that the country is immune to attacks like those also claimed by Islamic State in neighboring France.

Munich was the scene of the bloodiest of the German attacks, on July 22, in which an 18-year-old German-Iranian gunman killed nine people. The gunman’s father told the Bild am Sonntag weekly newspaper that he and his wife had since received death threats: “Our life in Munich is done,” he said.

Two of the assailants in the other attacks, a Syrian asylum seeker who blew himself up in Ansbach and a refugee from either Pakistan or Afghanistan who attacked people on a train in Bavaria, had links to Islamist militancy, officials say. The Munich gunman did not.

Critics of Chancellor Angela Merkel have blamed the attacks on her open-door refugee policy, under which over a million migrants, many fleeing war in Afghanistan, Syria and Iraq, entered Germany in the past year.

Merkel, who attended Sunday’s memorial but has faced media criticism for not visiting the attack scenes, set out a nine-point plan on Thursday to respond to the attacks, including an early warning system for the radicalization of refugees.

Gauck said he understood why many Germans were shaken after the attacks, but Germany would not submit to the assailants.

“They won’t compel us to hate, like they hate,” he said. “They won’t hold us in the confinement of perpetual fear. We will remain what we are: a considerate, supportive society.”