German police lead arriving migrants across a field to a transport facility, in October last year | Johannes Simon/Getty images French PM says Merkel’s migration policy ‘unsustainable’

German Chancellor Angela Merkel's open doors migration policy is not sustainable in the long run, Manuel Valls, France's prime minister, said.

"This policy, which is justified temporarily, is unsustainable in the long term," Valls told German regional media group Funke in an interview to be published Saturday.

"We have to say this clearly: Europe cannot take in all migrants from Syria, Iraq or Africa. It has to regain control over its borders, over its migration or asylum policies," said Valls, before heading to the Munich Security Conference.

Valls' criticism came a day after Russian Prime Minister Dmitry Medvedev described Merkel's migration policy as "stupid."

Merkel is under pressure on the home front too. In a poll for public broadcaster ARD and the newspaper Die Welt, released on Wednesday night, 46 percent of respondents said they were satisfied with Merkel’s performance — down from 75 percent less than a year ago, in April 2015.