By Jens Hack and Paul Carrel

MUNICH/BERLIN (Reuters) - Bavaria's premier, whose state bore the brunt of recent attacks in Germany, took aim at Chancellor Angela Merkel's open-door refugee policy on Saturday by rejecting her "we can do this" mantra.

The comments from Horst Seehofer, whose Christian Social Union is the Bavarian sister party of Merkel's conservatives, exacerbate the chancellor's difficulty in standing by a policy that her critics have blamed for the attacks and which risks undermining her popularity before federal elections next year.

"'We can do this' - I cannot, with the best will, adopt this phrase as my own," Seehofer told reporters after a meeting of his party.

Five attacks in Germany since July 18 have left 15 people dead, including four assailants, and dozens injured. Two of the attackers had links to Islamist militancy, officials say. Germany is wrestling with how to respond.

Jens Spahn, deputy finance minister and a senior member of Merkel's conservatives, said that integrating the refugees was a Herculean task but the government needed to put more pressure on those new arrivals unwilling to make an effort to fit in.

"A ban on the full body veil - that is the niqab and the burka - is overdue," he told daily Die Welt. "My impression is that we all underestimated a year ago what would come upon us with this big refugee and migration movement."

Over a million migrants have entered Germany in the past year, many fleeing war in Afghanistan, Syria and Iraq.

In an editorial, magazine Der Spiegel noted that the government of Helmut Schmidt, who served as chancellor from 1974 to 1982, toughened laws to combat the ultra-leftist Red Army Faction, which attacked the political and business elite, but added: "the terrorists nonetheless carried on bombing."

The comments from Seehofer, who said following the latest attacks that "all our predictions have been proven right", came after Merkel on Thursday defiantly repeated "we can do this" and vowed not to bend her refugee policy.

"The problem is too big for that and the attempts at a solution thus far too unsatisfactory," said Seehofer. "Restrictions on immigration are a condition for security in this country."

Merkel on Thursday set out a nine-point plan to respond to the attacks, including an early warning system for the radicalisation of refugees.

She faced criticism on social media after failing to react until the next day to the bloodiest of the attacks, in Munich, where an 18-year-old German-Iranian gunman killed nine people.

(Reporting by Jens Hack; Writing by Paul Carrel; Editing by Dale Hudson)