Germany's arrest of an Islamic State sleeper cell this week has prompted a fierce critic of Chancellor Angela Merkel to say she is reaping the harvest of her open door immigration policy.

'This is the revenge for blatant gaps in control of the huge stream of refugees into Germany, particularly in the autumn of last year,' said Bavarian interior minister Joachim Herrmann.

Herrmann, a member of the CSU party which Mrs Merkel's CDU needs on her side to govern the country, went on: 'Thousands of people came to Germany without adequately verified identities.

'We now know that ISIS purposefully took advantage of these vulnerabilities to camouflage assassins as refugees'.

Germany's arrest of an Islamic State sleeper cell this week has prompted a fierce critic of Chancellor Angela Merkel (pictured) to say she is reaping the harvest of her open door immigration policy

He was speaking out after special anti-terror police swooped on two refugee homes and three apartments on Tuesday to arrest three men linked to the Paris attackers of November last year.

The men were described by German interior minister Thomas de Maziere as a sleeper cell probably awaiting orders from Islamic State commanders in Syria to carry out atrocities in Germany.

The men were equipped with false passports by ISIS forgers, given tens of thousands of American dollars and had special communications equipment linking them to their commanders into their mobile telephones.

Herrmann said it was now vital for authorities to check all the details of every single migrant in the country to prevent more plots being hatched by militants among the refugees.

German intelligence chiefs believe there are at least 520 fanatics among the 1.2 million asylum seekers plotting to bring carnage to the country.

Hermann said: 'We need strict border controls and to know the real identities of those who come to us in this country'.