BERLIN (AFP) - German police on Thursday (Feb 4) arrested two Algerians suspected of links to the Islamic State in Iraq and Syria (ISIS) group after raids targeting several sites, including refugee shelters where some of the suspects lived.
They and two other Algerians "from the jihadist scene are under investigation over suspicions that they are planning a serious act threatening the security of the state", Berlin police said.
The men were suspected of planning a possible strike against the German capital, a spokesman for Berlin prosecutors told AFP, but did not confirm national media reports that the Alexanderplatz transport and shopping hub was the target.
The alleged involvement of Algerians in an ISIS plot and the link to refugee shelters, is expected to add fuel to a raging debate over the 1.1 million asylum seekers that Germany took in last year.
North African migrants have already been in the spotlight after they were blamed for a rash of sexual assaults during New Year Eve's festivities in the western German city of Cologne.
But the latest arrests risk compounding fears that militants are taking advantage of the massive influx of asylum seekers to slip into Europe undetected.
The operation came as a huge police deployment was underway in Cologne to avoid a repeat of the New Year's Eve attacks during the week-long carnival festivities which begin Thursday (Feb 4).
One of the two men captured on Thursday (Feb 4) is wanted by Algerian authorities for his links to ISIS, police said, adding that "investigations show that he has been trained militarily in Syria". The suspect had arrived in Germany last autumn, and was registered as an asylum seeker, according to national news agency DPA.
A woman detained in the course of the raids is the suspect's wife, police said.
The second Algerian man was arrested for having falsified identity documents.
Police officers tracked down the two other suspects but did not arrest them.
Some 450 officers took part in the operation in Berlin and the states of North Rhine-Westphalia and Lower Saxony, and seized computers and mobile telephones.
Among the locations searched were "the refugee shelters where the suspects lived", Berlin police spokesman Stefan Redlich told news channel N24.
He also told a news conference that two of the four suspects had sought to pass themselves off as Syrians.
In Berlin, police officers led away a man who had his head covered with a towel, according to an AFP photographer at the scene.
No weapons were found in the operation, Mr Redlich said, but Bild newspaper said that investigators were searching for explosives.
Berlin's home affairs chief Frank Henkel said the "level of threat posed by Islamist militants remains high".
"We have every reason to remain vigilant and careful. Therefore there should be a systematic crackdown on the Islamist scene, especially if there are likely links to IS," he said, referring to ISIS.
Since the November attacks in Paris, which killed 130 people and were claimed by ISIS, German authorities have issued terror alerts on several occasions.
In November, a Germany-Netherlands football match was called off, and on New Year's Eve, several Munich railway stations were closed over such threats.