BERLIN (Reuters) – German forces arrested two men on Thursday suspected of links to Islamic State militants preparing an attack in the German capital, police and prosecutors said, amid fears of another deadly attack on European soil.

Police and special forces raided four flats and two offices in Berlin and properties in the northern regions of North Rhine-Westphalia and Lower Saxony.

“Specifically (the raids) concern possible plans for an attack in Germany, even more specifically in Berlin,” Martin Steltner, a spokesman for Berlin prosecutors, told Reuters TV.

Berlin police spokesman Stefan Redlich said the authorities were investigating four Algerian men. Police detained two men and a woman.

“Our understanding is that the four men accused could have planned to carry out such an attack together,” Steltner said.

German media reported that central Berlin landmarks and tourist attractions Checkpoint Charlie and Alexanderplatz were targets.

Redlich said the Berlin suspects worked in those two locations and that searches were carried out there. But he could not confirm that they were the targets.

Redlich and Steltner said police acted on a tip-off but gave no further details.

Security agencies have been monitoring the suspects since January, Funke Media Group said. The men behaved conspiratorially, changed their mobile phones multiple times and communicated via instant messaging services, it added.

The Tagesspiegel newspaper, citing security sources, said leading members of Islamic State (IS), who were responsible for the Paris attacks that killed 130 people in November, had given the order for an attack in Germany.

Prosecutors declined to comment on the report.

‘NO SMOKING GUN’

Police seized computers, mobile telephones and sketches in the raids, Steltner said, adding “we haven’t found the smoking gun”.

A couple was arrested in North Rhine-Westphalia and another man was arrested in Berlin, Steltner said. All were detained on existing warrants related to other matters.

The man detained in North-Rhine Westphalia was arrested in a shelter for refugees and arrived a short while ago in Germany claiming to be from Syria, Steltner said.

He is wanted by Algerian authorities, who believe he is a member of Islamic State, said Steltner. He is suspected of having military training in Syria.

The status of the other men was unclear, but Redlich said the two Berlin-based suspects were not refugees.

“In Berlin, the two persons we are investigating are not refugees,” Redlich added. “Both have jobs here and have been here a long time.”

German fears about an attack have risen since the Paris killings. Authorities canceled a friendly international soccer match in Hanover last year and closed stations in Munich at New Year due to security concerns.

(Additional reporting by Madeline Chambers, Victoria Bryan and Paul Carrel in Berlin and Matthias Inverardi in Duesseldorf; Editing by Larry King and Katharine Houreld)