Public backing for a German far-right party is at its most popular in its history - just days after it said Islam was incompatible with the country's constitution.

Opinion polls have given Alternative for Germany (AfD) support of 15 per cent - gaining significant ground on Chancellor Angela Merkel's main coalition partner, the centre-left Social Democrats.

Formed only three years ago on a eurosceptic platform, AfD is now Germany's third strongest party, according to a recent survey.

Public backing for Germany's far-right party AfD is at its most popular in its history - just days after it said Islam was incompatible with the country's constitution. AfD members are pictured voting on Saturday

The statistics were revealed as Merkel today urged European leaders to protect the EU's external borders or risk a 'return to nationalism'.

She said today that border defence represents a 'challenge for the future of Europe' from 'the Mediterranean to the North Pole'.

Merkel said earlier this week that the rise of the far-right in Germany was a phenomenon that 'we have to deal with'.

'We see that there are political forces with very negative rhetoric on Europe,' she said, referring to AfD.

'We have to ensure that Europe is a project that people understand,' she said, adding that a key message that has to hit home is that 'it's better with Europe than without Europe'.

The statistics were revealed as Angela Merkel (pictured) today urged European leaders to protect the EU's external borders or risk a 'return to nationalism'

The populist upstart outfit has shifted its rhetoric to one that rails against the influx of 1.1million asylum seekers in 2015, and last weekend adopted an anti-Islam platform.

German politicians from across the spectrum criticised the anti-immigration party on Monday after it declared Islam incompatible with the constitution.

The AfD backed a manifesto pledge at a congress on Sunday to ban on minarets and the burqa, the full face and body-covering gown worn by some Muslim women.

It has no lawmakers in the federal parliament in Berlin but has members in half of Germany's 16 regional state assemblies.

Merkel has said freedom of religion for all is guaranteed by Germany's constitution and that Islam is a part of Germany.