German Vice Chancellor Sigmar Gabriel said in an interview on Saturday that Chancellor Angela Merkel's conservatives had "underestimated" the challenge of integrating record numbers of migrants.
Gabriel leads the Social Democrats (SPD) -- the junior coalition partner in Merkel's government -- and his comments come as campaigning kicks off for a federal election next year and regional elections in Berlin and the eastern state of Mecklenburg-Vorpommern.
Hundreds of thousands of migrants arrived in Germany from the Middle East, Africa and elsewhere last year. There is widespread concern about how to integrate them into German society and the labour market, and support for the anti-immigrant party Alternative for Germany (AfD) has grown.
"I, we always said that it's inconceivable for Germany to take in a million people every year," Gabriel said in an interview with broadcaster ZDF. "There is an upper limit to a country's integration ability," he added at a news conference on Sunday.
He said Germany had 300,000 new school children due to the migrant influx and added that the country could not manage to integrate so many into the school system every year because there would not be enough teachers.