Merkel faces backlash after killings

“People are scared, completely understandably, and right now they need a credible answer from politicians,” said minister president of Bavaria Horst Seehofer, adding that it was “finally time to address people’s fears”.

Seehofer, leader of CSU, the sister party to Merkel's CDU, has long been critical of Merkel's migration policy and now criticises her for "dodging the issue".

The “policy of open borders cannot be tolerated any more”, he said, adding that terrorists were “using the [refugee] routes to enter Germany”.

Merkel has tried to project calm, staying put in her summer cottage.

But due to the mounting pressure on her, she has called for a news conference for Thursday.

Merkel's government is arguing that three of the four assailants arrived in Germany before the chancellor's decision to open Germany's borders.

The fourth killer, a teenager who went on a shooting rampage in Munich on Friday, was born and raised in Germany, the son of Iranian asylum seekers who arrived in the 1990s. Investigators ruled out an Islamist motive in that case.

At a joint press conference with Seehofer on Tuesday, Bavarian interior minister Joachim Herrmann said he would push to allow the German army to be deployed within the country in the case of future attacks.

They also argued for making it easier to deport asylum seekers, even to war zones, if they have committed criminal offences.

Herrmann also said no asylum seeker should be allowed into Germany if they cannot prove their identity.

"What we always warned of has now happened," Frauke Petry, leader of the right-wing populist AfD party, said in a statement after the killings.

The AfD, which has gained support on an anti-Islam stance, aims to make a strong showing in the polls in Mecklenburg-Western Pomerania on 4 September.

An AfD win would deal a powerful blow to Merkel a year before the general elections.