Merkel's premiership is hanging by a thread today as thousands gathered to call for her resignation while a key political ally dramatically withdrew his support over immigration policy.

More than 5,000 protested in Berlin and thousands more throughout Germany over the 'open-door' policy that many have blamed for four brutal terrorist attacks that left 13 dead over the last month.

The Chancellor faced a fresh wave of fury after it emerged that two recent terror attacks and a third killing were carried out by men who entered the country as refugees.

Despite the massive waves of criticism, Merkel defended her policy this week, dramatically proclaiming 'we can do it' as she pledged not to let the violent acts guide political decisions.

But now her key ally in Bavaria - which bore the brunt of the attacks - has launched a fresh attack on her leadership, distancing his party from Merkel and straining the coalition that keeps her in power.

Horst Seehofer, the conservative premier of Bavaria, said he did not share Merkel's 'we can do it' credo on accommodating the almost 1.1 million migrants and refugees who arrived in 2015.

Seehofer, who leads the Christian Social Union, the sister party to Merkel's conservative Christian Democrats, said today '"We can do this" - I cannot, with the best will, adopt this phrase as my own.'