BERLIN (AP) — Top security officials in Germany called Tuesday for tougher security screening of asylum-seekers and also announced that more police officers would be hired following four attacks in the country in the span of a week — two of them claimed by the extremist Islamic State group.

Horst Seehofer, the governor of Bavaria — where three of last week’s attacks took place — told the daily Sueddeutsche Zeitung Tuesday: “We must know who is in our country.”

Thomas Strobl, the interior minister of Baden-Wuerttemberg, where a woman was killed by a Syrian attacker Sunday, also demanded a tougher stance toward asylum-seekers.

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“Those who abuse the right to hospitality must go back to their home countries — make no mistake about it,” Strobl told Funke media group.

Three of the attacks were carried out by recent immigrants, rekindling concerns about Germany’s ability to cope with the estimated 1 million migrants registered entering the country last year.

Seehofer also announced that the state of Bavaria would hire more police officers.

“The increase will be significant,” he said.

In the most recent attack, a 27-year-old Syrian asylum-seeker set off a backpack laden with explosives and shrapnel Sunday night after being refused entry to a crowded music festival in the Bavarian city of Ansbach, killing himself and wounding 15 people.

The extremist Islamic State group published a video early Tuesday in which a man pledges allegiance to IS and vows Germany’s people “won’t be able to sleep peacefully anymore.” It appears to be the same as the one found by German investigators on the suicide bomber’s phone.

The man, believed to be the bombing suspect, whose name authorities have confirmed as Mohammad Daleel, appears on the video with his face covered with a black scarf, threatens to make life intolerable and that “we will blow up your homes.” German authorities could not immediately be reached to confirm whether the video was the same.

On the video the attacker said he acted in response to the extremist group’s call to target countries of the US-led coalition fighting it in Iraq and Syria. Germany is not involved in combat operations but has contributed reconnaissance aircraft to the effort.

He threatened that the group would carry out more violence after the bombing in Ansbach, saying “this blessed operation will be followed by others.”

After the IS connection surfaced, federal prosecutors in Karlsruhe, who investigate all suspected terrorism, took over the case saying they would seek to “determine if thus-far unknown accomplices or backers were involved in the crime.”

A spokeswoman for the federal prosecutor’s office told The Associated Press that “a main focus is on the question of whether the attacker in Ansbach was helped in the planning and preparation.” She spoke on condition of anonymity in line with department policy.

Investigators also need to determine how the video from the attacker got to IS and where he learned to build a bomb.

The suspect, who is originally from the Syrian city of Aleppo, came to Germany two years ago and applied for asylum in August 2014, Interior Minister Thomas de Maiziere said. It turned out that he had already registered in Bulgaria and later in Austria, so Germany rejected his request and ordered him deported to Bulgaria — most recently on July 13.

Asylum-seekers are routinely deported to the first country where they registered if they don’t follow proper procedures, even if they’re considered to have a legitimate asylum claim.

Copyright 2016 The Associated Press