Germany announces indefinite border checks

"I don't foresee a moment when we can end it," he said.

De Maiziere's announcement follows heightened tensions over Merkel's open asylum policy as her fiercest domestic critic, Bavarian prime minister Horst Seehofer, demanded a sharp reduction of refugee numbers within the "next few weeks".

Seehofer, who heads the Christian-Social Union (CSU), earlier this week demanded results before March. The CSU is the Bavarian sister party to Merkel's Christian-Democrats (CDU).

Controls 'not the solution'

Germany is hosting more than 1 million refugees and asylum seekers. Some 40% are fleeing conflict in Syria.

An average of 3,000 are arriving every day, down from a peak of about 10,000 last year.

De Maiziere's announcement to keep border checks for an indefinite period marks a departure from foreign minister Frank-Walter Steinmeier.

Steinmeier, a centre-left Social-Democrat, said closing borders would not solve the issue.

"I guarantee you that 'a solution to the crisis' will not be achieved through a closure of the border," he said.

Steinmeier's response came after Germany's transport minister criticised Merkel's policy.

Meanwhile Merkel, who faces the biggest challenge in her political career, has reportedly denounced moves by neighbouring Austria to impose a cap on the number of asylum claims.

Austrian chancellor Werner Faymann said the number of claims would be limited to 1.5% of the Austrian population over the next four years.

The Austrian border clamp down is already having knock-on effects elsewhere with Macedonia sealing its border with Greece.

Authorities in Serbia and Croatia say they would only allow people through who were seeking asylum in Austria and Germany.

Slovenia, which borders Austria to the south, is likely to send troops to the border with Croatia.

Schengen six-month rule

Germany first imposed a ten-day control at its Austrian border at the start of September after having announced an open door policy for Syrian nationals.

It then extended it to 20 days and then again for another 20 days.

It now wants to maintain the controls, but EU rules allow for border checks for only six months.

The limit can be extended to two years if EU institutional procedures and evaluations determine the gaps on the external frontiers somehow pose a major threat to the passport-free Schengen zone.

The EU Commission, for its part, said in December that it was probing Greek border holes and would submit a report to the Schengen Evaluation committee.