Germany's secret service has received more than 100 tip-offs that ISIS militants are hiding out among asylum seekers, it was reported today.

The head of the domestic intelligence agency (BfV), Hans-Georg Maassen, mentioned the figure at a discussion in the Interior Ministry, according to local media.

It comes a day after police conducted raids on suspected Islamist militants at locations across the country, including two refugee centres.

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Hunted down: Police officers escort an Islamist terror suspect from a flat during a raid in Berlin. German police have carried out raids on locations across Germany, including two refugee centres, as part of an investigation into four Algerian men suspected of planning attacks on the country

But Mr Maassen also said that among those tip-offs there were some cases of untruthful defamation, the Berliner Zeitung newspaper reported, without citing sources.

The BfV was not immediately available for comment when contacted by Reuters news agency.

Two men and a woman were arrested during massive police raids in the hunt for four Algerians being sought for their suspected links with ISIS in Syria.

Refugee shelters in Hanover and Attendorn and addresses in Berlin were among a series of dawn swoops.

Berlin police said the four 'from the jihad scene are under investigation over suspicions that they are planning a serious act threatening the security of the state'.

See ISIS news as Germany is tipped-off that ISIS militants are among migrants

German anti-terror police officers leave an apartment following a raid in Hanover, Germany, as part of an investigation into four Algerian men suspected of planning attacks in Germany and having ties to ISIS

The three arrested were the subject of existing warrants.

Police said one man is wanted for belonging to ISIS by the Algerian authorities who say he was trained in Syria. His wife was also detained.

The other man was arrested for having fake ID documents.

Experts say Germany is long overdue a terrorist attack by jihadists because of its support for military operations against the group in Iraq and Syria.

Critics have long argued that Chancellor Merkel's open door policy towards refugees could allow terrorists to come into Germany posing as refugees from war and terror.